Code restructured, and it's now using Pyparsing

3 files changed, 1071 insertions, 807 deletions

diff --git a/LICENSE b/LICENSE
index ea94979..b3b18a4 100644
--- a/LICENSE
+++ b/LICENSE
@@ -1,5 +1,6 @@
 The MIT License
 
+Copyright (c) 2011 German M. Bravo (Kronuz)
 Copyright (c) 2010 Anton Pawlik
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
diff --git a/README.rst b/README.rst
index f6218c5..56f19dd 100644
--- a/README.rst
+++ b/README.rst
@@ -8,16 +8,118 @@ xCSS for Python
 About
 =====
 xCSS for Python is a superset of CSS that is more powerful, elegant and easier
-to maintain than plain-vanilla CSS. The framework works as a CSS source code
-preprocesor which allows you to use variables, nested rules, mixins, and extend
-classes, all with a CSS-compatible syntax which the preprocessor then compiles
-to standard CSS.
+to maintain than plain-vanilla CSS. The library works as a CSS source code
+preprocesor which allows you to use variables, nested rules, mixins, and have
+inheritance of rules, all with a CSS-compatible syntax which the preprocessor
+then compiles to standard CSS.
 
 xCSS, as an extension of CSS, helps keep large stylesheets well-organized. It
 borrows concepts and functionality from projects such as OOCSS and other similar
 frameworks like as Sass. It's build on top of the original PHP xCSS codebase
 structure but it's been completely rewritten and many bugs have been fixed.
 
+Usage
+=====
+# **Nested Rules**
+Example:
+	.selector {
+	    a {
+	        display: block;
+	    }
+	    strong {
+	        color: blue;
+	    }
+	}
+...produces:
+	.selector a {
+	    display: block;
+	}
+	.selector strong {
+	    color: #00f;
+	}
+
+# **Variables**
+Example:
+	$main-color: #ce4dd6;
+	$style: solid;
+        $side: bottom;
+	#navbar {
+	  border-#{$side}: {
+	    color: $main-color;
+	    style: $style;
+	  }
+	}
+...produces:
+	#navbar {
+		border-bottom-color: #ce4dd6;
+		border-bottom-style: solid;
+	}
+
+# **Mixins**
+Example:
+	@mixin rounded($side, $radius: 10px) {
+	  border-#{$side}-radius: $radius;
+	  -moz-border-radius-#{$side}: $radius;
+	  -webkit-border-#{$side}-radius: $radius;
+	}
+	#navbar li { @include rounded(top); }
+	#footer { @include rounded(top, 5px); }
+	#sidebar { @include rounded(left, 8px); }
+...produces:
+	#navbar li {
+		border-top-radius: 10px;
+		-moz-border-radius-top: 10px;
+		-webkit-border-top-radius: 10px;
+	}
+	#footer {
+		border-top-radius: 5px;
+		-moz-border-radius-top: 5px;
+		-webkit-border-top-radius: 5px;
+	}
+	#sidebar {
+		border-left-radius: 8px;
+		-moz-border-radius-left: 8px;
+		-webkit-border-left-radius: 8px;
+	}
+
+# **Extend** (using `@extend`)
+Example:
+	.error {
+	  border: 1px #f00;
+	  background-color: #fdd;
+	}
+	.error.intrusion {
+	  background-image: url("/image/hacked.png");
+	}
+	.seriousError {
+	  @extend .error;
+	  border-width: 3px;
+	}
+...produces:
+	.error,
+	.seriousError {
+		border: 1px red;
+		background-color: #fdd;
+	}
+	.error.intrusion,
+	.seriousError.intrusion {
+		background-image: url("/image/hacked.png");
+	}
+	.seriousError {
+		border-width: 3px;
+	}
+
+Usage
+=====
+	from xcss import xCSS
+	css = xCSS()
+	css.compile("a { color: red + green; }")
+
+Installation Notes
+==================
+It requires the Pyparsing module from:
+http://pyparsing.wikispaces.com/
+
 License
 =======
 MIT License. See *LICENSE* for details.
diff --git a/xcss.py b/xcss.py
index efa1f08..210a1f5 100644
--- a/xcss.py
+++ b/xcss.py
@@ -5,7 +5,7 @@ xCSS Framework for Python
 
 @author    German M. Bravo (Kronuz)
            Based on some code from the original xCSS project by Anton Pawlik
-@version   0.2
+@version   0.3
 @see       http://xcss.antpaw.org/docs/
            http://sass-lang.com/
            http://oocss.org/spec/css-object-model.html
@@ -15,10 +15,10 @@ xCSS Framework for Python
            http://www.opensource.org/licenses/mit-license.php
 
 xCSS for Python is a superset of CSS that is more powerful, elegant and easier
-to maintain than plain-vanilla CSS. The framework works as a CSS source code
-preprocesor which allows you to use variables, nested rules, mixins, and extend
-classes, all with a CSS-compatible syntax which the preprocessor then compiles
-to standard CSS.
+to maintain than plain-vanilla CSS. The library works as a CSS source code
+preprocesor which allows you to use variables, nested rules, mixins, and have
+inheritance of rules, all with a CSS-compatible syntax which the preprocessor
+then compiles to standard CSS.
 
 xCSS, as an extension of CSS, helps keep large stylesheets well-organized. It
 borrows concepts and functionality from projects such as OOCSS and other similar
@@ -29,7 +29,187 @@ structure but it's been completely rewritten and many bugs have been fixed.
 
 import re
 import sys
-from math import *
+
+from django.utils.datastructures import SortedDict
+
+# units and conversions
+_units = ['em', 'ex', 'px', 'cm', 'mm', 'in', 'pt', 'pc', 'deg', 'rad'
+          'grad', 'ms', 's', 'hz', 'khz', '%']
+_conv = {
+    'size': {
+        'em': 13.0,
+        'px': 1.0
+    },
+    'length': {
+        'mm':  1.0,
+        'cm':  10.0,
+        'in':  25.4,
+        'pt':  25.4 / 72,
+        'pc':  25.4 / 6
+    },
+    'time': {
+        'ms':  1.0,
+        's':   1000.0
+    },
+    'freq': {
+        'hz':  1.0,
+        'khz': 1000.0
+    }
+}
+_conv_mapping = {}
+for t, m in _conv.items():
+    for k in m:
+        _conv_mapping[k] = t
+del t, m, k
+
+# color literals
+_colors = {
+    'aliceblue': '#f0f8ff',
+    'antiquewhite': '#faebd7',
+    'aqua': '#00ffff',
+    'aquamarine': '#7fffd4',
+    'azure': '#f0ffff',
+    'beige': '#f5f5dc',
+    'bisque': '#ffe4c4',
+    'black': '#000000',
+    'blanchedalmond': '#ffebcd',
+    'blue': '#0000ff',
+    'blueviolet': '#8a2be2',
+    'brown': '#a52a2a',
+    'burlywood': '#deb887',
+    'cadetblue': '#5f9ea0',
+    'chartreuse': '#7fff00',
+    'chocolate': '#d2691e',
+    'coral': '#ff7f50',
+    'cornflowerblue': '#6495ed',
+    'cornsilk': '#fff8dc',
+    'crimson': '#dc143c',
+    'cyan': '#00ffff',
+    'darkblue': '#00008b',
+    'darkcyan': '#008b8b',
+    'darkgoldenrod': '#b8860b',
+    'darkgray': '#a9a9a9',
+    'darkgreen': '#006400',
+    'darkkhaki': '#bdb76b',
+    'darkmagenta': '#8b008b',
+    'darkolivegreen': '#556b2f',
+    'darkorange': '#ff8c00',
+    'darkorchid': '#9932cc',
+    'darkred': '#8b0000',
+    'darksalmon': '#e9967a',
+    'darkseagreen': '#8fbc8f',
+    'darkslateblue': '#483d8b',
+    'darkslategray': '#2f4f4f',
+    'darkturquoise': '#00ced1',
+    'darkviolet': '#9400d3',
+    'deeppink': '#ff1493',
+    'deepskyblue': '#00bfff',
+    'dimgray': '#696969',
+    'dodgerblue': '#1e90ff',
+    'firebrick': '#b22222',
+    'floralwhite': '#fffaf0',
+    'forestgreen': '#228b22',
+    'fuchsia': '#ff00ff',
+    'gainsboro': '#dcdcdc',
+    'ghostwhite': '#f8f8ff',
+    'gold': '#ffd700',
+    'goldenrod': '#daa520',
+    'gray': '#808080',
+    'green': '#008000',
+    'greenyellow': '#adff2f',
+    'honeydew': '#f0fff0',
+    'hotpink': '#ff69b4',
+    'indianred': '#cd5c5c',
+    'indigo': '#4b0082',
+    'ivory': '#fffff0',
+    'khaki': '#f0e68c',
+    'lavender': '#e6e6fa',
+    'lavenderblush': '#fff0f5',
+    'lawngreen': '#7cfc00',
+    'lemonchiffon': '#fffacd',
+    'lightblue': '#add8e6',
+    'lightcoral': '#f08080',
+    'lightcyan': '#e0ffff',
+    'lightgoldenrodyellow': '#fafad2',
+    'lightgreen': '#90ee90',
+    'lightgrey': '#d3d3d3',
+    'lightpink': '#ffb6c1',
+    'lightsalmon': '#ffa07a',
+    'lightseagreen': '#20b2aa',
+    'lightskyblue': '#87cefa',
+    'lightslategray': '#778899',
+    'lightsteelblue': '#b0c4de',
+    'lightyellow': '#ffffe0',
+    'lime': '#00ff00',
+    'limegreen': '#32cd32',
+    'linen': '#faf0e6',
+    'magenta': '#ff00ff',
+    'maroon': '#800000',
+    'mediumaquamarine': '#66cdaa',
+    'mediumblue': '#0000cd',
+    'mediumorchid': '#ba55d3',
+    'mediumpurple': '#9370db',
+    'mediumseagreen': '#3cb371',
+    'mediumslateblue': '#7b68ee',
+    'mediumspringgreen': '#00fa9a',
+    'mediumturquoise': '#48d1cc',
+    'mediumvioletred': '#c71585',
+    'midnightblue': '#191970',
+    'mintcream': '#f5fffa',
+    'mistyrose': '#ffe4e1',
+    'moccasin': '#ffe4b5',
+    'navajowhite': '#ffdead',
+    'navy': '#000080',
+    'oldlace': '#fdf5e6',
+    'olive': '#808000',
+    'olivedrab': '#6b8e23',
+    'orange': '#ffa500',
+    'orangered': '#ff4500',
+    'orchid': '#da70d6',
+    'palegoldenrod': '#eee8aa',
+    'palegreen': '#98fb98',
+    'paleturquoise': '#afeeee',
+    'palevioletred': '#db7093',
+    'papayawhip': '#ffefd5',
+    'peachpuff': '#ffdab9',
+    'peru': '#cd853f',
+    'pink': '#ffc0cb',
+    'plum': '#dda0dd',
+    'powderblue': '#b0e0e6',
+    'purple': '#800080',
+    'red': '#ff0000',
+    'rosybrown': '#bc8f8f',
+    'royalblue': '#4169e1',
+    'saddlebrown': '#8b4513',
+    'salmon': '#fa8072',
+    'sandybrown': '#f4a460',
+    'seagreen': '#2e8b57',
+    'seashell': '#fff5ee',
+    'sienna': '#a0522d',
+    'silver': '#c0c0c0',
+    'skyblue': '#87ceeb',
+    'slateblue': '#6a5acd',
+    'slategray': '#708090',
+    'snow': '#fffafa',
+    'springgreen': '#00ff7f',
+    'steelblue': '#4682b4',
+    'tan': '#d2b48c',
+    'teal': '#008080',
+    'thistle': '#d8bfd8',
+    'tomato': '#ff6347',
+    'turquoise': '#40e0d0',
+    'violet': '#ee82ee',
+    'wheat': '#f5deb3',
+    'white': '#ffffff',
+    'whitesmoke': '#f5f5f5',
+    'yellow': '#ffff00',
+    'yellowgreen': '#9acd32'
+}
+
+def float2str(num):
+    if isinstance(num, float):
+        return ('%0.04f' % num).rstrip('0').rstrip('.')
+    return str(num)
 
 FILEID = 0
 POSITION = 1
@@ -40,49 +220,6 @@ OPTIONS = 5
 SELECTORS = 6
 PROPERTIES = 7
 
-def safe_eval(str, context=None):
-    # Safe eval:
-
-    #make a list of safe functions
-    safe_locals = ['math','acos', 'asin', 'atan', 'atan2', 'ceil', 'cos',
-                   'cosh', 'degrees', 'e', 'exp', 'fabs', 'floor', 'fmod',
-                   'frexp', 'hypot', 'ldexp', 'log', 'log10', 'modf', 'pi',
-                   'pow', 'radians', 'sin', 'sinh', 'sqrt', 'tan', 'tanh']
-    safe_builtins = ['abs', 'max', 'min', 'int', 'pow']
-
-    safe_dict = {}
-
-    # use the list to filter the local namespace
-    safe_dict.update(dict([ (k, globals().get(k, None)) for k in safe_locals ]))
-
-    # add any needed builtins back in
-    safe_dict.update(dict([ (k, getattr(__builtins__, k, None)) for k in safe_builtins ]))
-
-    # add user context
-    safe_dict.update(context or {})
-
-    return eval(str, {"__builtins__": None}, safe_dict)
-
-
-# this does not increase asymptotical complexity
-# but can still waste more time than it saves. TODO: profile
-# from http://stackoverflow.com/questions/2892931/longest-common-substring-from-more-than-two-strings-python
-def long_substr(strings):
-    substr = ""
-    if not strings:
-        return substr
-    reference = min(strings, key=len) #strings[0]
-    length = len(reference)
-    #find a suitable slice i:j
-    for i in xrange(length):
-        #only consider strings long at least len(substr) + 1
-        for j in xrange(i + len(substr) + 1, length + 1):
-            candidate = reference[i:j]  # is the slice recalculated every time?
-            if all(candidate in text for text in strings):
-                substr = candidate
-    return substr
-
-
 class xCSS(object):
     # configuration:
     construct = 'self'
@@ -92,180 +229,6 @@ class xCSS(object):
     #optinos
     verbosity = 0
 
-    # units and conversions
-    _units = ['em', 'ex', 'px', 'cm', 'mm', 'in', 'pt', 'pc', 'deg', 'rad'
-              'grad', 'ms', 's', 'hz', 'khz', '%']
-    _conv = {
-        'size': {
-            'em': 13.0,
-            'px': 1.0
-        },
-        'length': {
-            'mm':  1.0,
-            'cm':  10.0,
-            'in':  25.4,
-            'pt':  25.4 / 72,
-            'pc':  25.4 / 6
-        },
-        'time': {
-            'ms':  1.0,
-            's':   1000.0
-        },
-        'freq': {
-            'hz':  1.0,
-            'khz': 1000.0
-        }
-    }
-    _conv_mapping = {}
-    for t, m in _conv.items():
-        for k in m:
-            _conv_mapping[k] = t
-    del t, m, k
-
-    # color literals
-    _colors = {
-        'aliceblue': '#f0f8ff',
-        'antiquewhite': '#faebd7',
-        'aqua': '#00ffff',
-        'aquamarine': '#7fffd4',
-        'azure': '#f0ffff',
-        'beige': '#f5f5dc',
-        'bisque': '#ffe4c4',
-        'black': '#000000',
-        'blanchedalmond': '#ffebcd',
-        'blue': '#0000ff',
-        'blueviolet': '#8a2be2',
-        'brown': '#a52a2a',
-        'burlywood': '#deb887',
-        'cadetblue': '#5f9ea0',
-        'chartreuse': '#7fff00',
-        'chocolate': '#d2691e',
-        'coral': '#ff7f50',
-        'cornflowerblue': '#6495ed',
-        'cornsilk': '#fff8dc',
-        'crimson': '#dc143c',
-        'cyan': '#00ffff',
-        'darkblue': '#00008b',
-        'darkcyan': '#008b8b',
-        'darkgoldenrod': '#b8860b',
-        'darkgray': '#a9a9a9',
-        'darkgreen': '#006400',
-        'darkkhaki': '#bdb76b',
-        'darkmagenta': '#8b008b',
-        'darkolivegreen': '#556b2f',
-        'darkorange': '#ff8c00',
-        'darkorchid': '#9932cc',
-        'darkred': '#8b0000',
-        'darksalmon': '#e9967a',
-        'darkseagreen': '#8fbc8f',
-        'darkslateblue': '#483d8b',
-        'darkslategray': '#2f4f4f',
-        'darkturquoise': '#00ced1',
-        'darkviolet': '#9400d3',
-        'deeppink': '#ff1493',
-        'deepskyblue': '#00bfff',
-        'dimgray': '#696969',
-        'dodgerblue': '#1e90ff',
-        'firebrick': '#b22222',
-        'floralwhite': '#fffaf0',
-        'forestgreen': '#228b22',
-        'fuchsia': '#ff00ff',
-        'gainsboro': '#dcdcdc',
-        'ghostwhite': '#f8f8ff',
-        'gold': '#ffd700',
-        'goldenrod': '#daa520',
-        'gray': '#808080',
-        'green': '#008000',
-        'greenyellow': '#adff2f',
-        'honeydew': '#f0fff0',
-        'hotpink': '#ff69b4',
-        'indianred': '#cd5c5c',
-        'indigo': '#4b0082',
-        'ivory': '#fffff0',
-        'khaki': '#f0e68c',
-        'lavender': '#e6e6fa',
-        'lavenderblush': '#fff0f5',
-        'lawngreen': '#7cfc00',
-        'lemonchiffon': '#fffacd',
-        'lightblue': '#add8e6',
-        'lightcoral': '#f08080',
-        'lightcyan': '#e0ffff',
-        'lightgoldenrodyellow': '#fafad2',
-        'lightgreen': '#90ee90',
-        'lightgrey': '#d3d3d3',
-        'lightpink': '#ffb6c1',
-        'lightsalmon': '#ffa07a',
-        'lightseagreen': '#20b2aa',
-        'lightskyblue': '#87cefa',
-        'lightslategray': '#778899',
-        'lightsteelblue': '#b0c4de',
-        'lightyellow': '#ffffe0',
-        'lime': '#00ff00',
-        'limegreen': '#32cd32',
-        'linen': '#faf0e6',
-        'magenta': '#ff00ff',
-        'maroon': '#800000',
-        'mediumaquamarine': '#66cdaa',
-        'mediumblue': '#0000cd',
-        'mediumorchid': '#ba55d3',
-        'mediumpurple': '#9370db',
-        'mediumseagreen': '#3cb371',
-        'mediumslateblue': '#7b68ee',
-        'mediumspringgreen': '#00fa9a',
-        'mediumturquoise': '#48d1cc',
-        'mediumvioletred': '#c71585',
-        'midnightblue': '#191970',
-        'mintcream': '#f5fffa',
-        'mistyrose': '#ffe4e1',
-        'moccasin': '#ffe4b5',
-        'navajowhite': '#ffdead',
-        'navy': '#000080',
-        'oldlace': '#fdf5e6',
-        'olive': '#808000',
-        'olivedrab': '#6b8e23',
-        'orange': '#ffa500',
-        'orangered': '#ff4500',
-        'orchid': '#da70d6',
-        'palegoldenrod': '#eee8aa',
-        'palegreen': '#98fb98',
-        'paleturquoise': '#afeeee',
-        'palevioletred': '#db7093',
-        'papayawhip': '#ffefd5',
-        'peachpuff': '#ffdab9',
-        'peru': '#cd853f',
-        'pink': '#ffc0cb',
-        'plum': '#dda0dd',
-        'powderblue': '#b0e0e6',
-        'purple': '#800080',
-        'red': '#ff0000',
-        'rosybrown': '#bc8f8f',
-        'royalblue': '#4169e1',
-        'saddlebrown': '#8b4513',
-        'salmon': '#fa8072',
-        'sandybrown': '#f4a460',
-        'seagreen': '#2e8b57',
-        'seashell': '#fff5ee',
-        'sienna': '#a0522d',
-        'silver': '#c0c0c0',
-        'skyblue': '#87ceeb',
-        'slateblue': '#6a5acd',
-        'slategray': '#708090',
-        'snow': '#fffafa',
-        'springgreen': '#00ff7f',
-        'steelblue': '#4682b4',
-        'tan': '#d2b48c',
-        'teal': '#008080',
-        'thistle': '#d8bfd8',
-        'tomato': '#ff6347',
-        'turquoise': '#40e0d0',
-        'violet': '#ee82ee',
-        'wheat': '#f5deb3',
-        'white': '#ffffff',
-        'whitesmoke': '#f5f5f5',
-        'yellow': '#ffff00',
-        'yellowgreen': '#9acd32'
-    }
-
     _default_xcss_vars = {
         # unsafe chars will be hidden as vars
         '$__doubleslash': '//',
@@ -300,83 +263,39 @@ class xCSS(object):
         _reverse_colors[rgba_k] = k
     _reverse_colors_re = re.compile(r'(?<!\w)(' + '|'.join(map(re.escape, _reverse_colors.keys()))+r')\b', re.IGNORECASE)
     _colors_re = re.compile(r'\b(' + '|'.join(map(re.escape, _colors.keys()))+r')\b', re.IGNORECASE)
-
-    _color_re = re.compile(r'''
-        (# RGB in the hex form (#RRGGBB):
-            (?<!\w)
-            \#
-                (?P<short_R>[a-f0-9])
-                (?P<short_G>[a-f0-9])
-                (?P<short_B>[a-f0-9])
-            \b
-        | # RGB in the hex form (#RRGGBB):
-            (?<!\w)
-            \#
-                (?P<long_R>[a-f0-9]{2})
-                (?P<long_G>[a-f0-9]{2})
-                (?P<long_B>[a-f0-9]{2})
-            \b
-        | # RGB using the rgb():
-            \b
-            rgb\(
-                \s*(?P<rgb_R>\d+)(?P<rgbX>%?)\s*,
-                \s*(?P<rgb_G>\d+)(?P=rgbX)\s*,
-                \s*(?P<rgb_B>\d+)(?P=rgbX)\s*
-            \)
-        | # RGBA using the rgba():
-            \b
-            rgba\(
-                \s*(?P<rgba_R>\d+)(?P<rgbaX>%?)\s*,
-                \s*(?P<rgba_G>\d+)(?P=rgbaX)\s*,
-                \s*(?P<rgba_B>\d+)(?P=rgbaX)\s*,
-                \s*(?P<rgba_A>\d+)(?P=rgbaX)\s*
-            \)
-        )
-    ''', re.IGNORECASE | re.VERBOSE)
+    
     _expr_re = re.compile(r'''
-        (?P<expr>
-            \#\{.*?\}
-        |
-            (?:
-                [[(][\][()\s]*
-            )?
-            [#%.\w]+                # Accept a variable or constant or number (preceded by spaces or parenthesis)
+        \#\{.*?\}
+    |
+        (?:
+            [[(][\][()\s]*
+        )?
+        [#%.\w]+                # Accept a variable or constant or number (preceded by spaces or parenthesis)
+        (?:
             (?:
-                (?:
-                    \(              # Accept either the start of a function call... ("function_call(")
-                |
-                    [\][()\s]*      # ...or an operation ("+-*/")
-                    (?:\s-\s|[+*/]) # (dash needs a surrounding space always)
-                )
-                [\][()\s]*          
-                [#%.\w]+            # Accept a variable or constant or number (preceded by spaces or parenthesis)
-            )*                      # ...take n arguments,
-            (?:
-                [\][()\s]*[\])]     # but then finish accepting any missing parenthesis and spaces
-            )?
-            (?!.*:)
-            (?=.*;)
-        )
-        (?P<unit>
-            \s*[;}]
-        |
-            \s*$
-        |
-            [^;}\s]+
-        |
-            \s
-        )
+                \(              # Accept either the start of a function call... ("function_call(")
+            |
+                [\][()\s]*      # ...or an operation ("+-*/")
+                (?:\s-\s|[+*/^]) # (dash needs a surrounding space always)
+            )
+            [\][()\s]*          
+            [#%.\w]+            # Accept a variable or constant or number (preceded by spaces or parenthesis)
+        )*                      # ...take n arguments,
+        (?:
+            [\][()\s]*[\])]     # but then finish accepting any missing parenthesis and spaces
+            [^;}\s]*
+        )?
+        (?!.*?:)
+        (?=.*?;)
     ''', re.VERBOSE)
     #_expr_re = re.compile(r'(\[.*?\])([\s;}]|$|.+?\S)') # <- This is the old method, required parenthesis around the expression
     _ml_comment_re = re.compile(r'\/\*(.*?)\*\/', re.DOTALL)
     _sl_comment_re = re.compile(r'(?<!\w{2}:)\/\/.*')
-    _unit_re = re.compile(r'(?<=(\s|\d))' + '|'.join(map(re.escape, _units)) + r'(?!\w)', re.IGNORECASE)
-    _full_unit_re = re.compile(r'([\d.]+)(' + '|'.join(map(re.escape, _units)) + r')?(?!\w)', re.IGNORECASE)
     _zero_units_re = re.compile(r'\b0(' + '|'.join(map(re.escape, _units)) + r')(?!\w)', re.IGNORECASE)
 
     _includes_re = re.compile(r'@include\s+(.*?)\s*(\((.+?,)*(.+?)\))?\s*([;}]|$)', re.DOTALL)
     _remove_decls_re = re.compile(r'(@option\b.*?([;}]|$))', re.DOTALL | re.IGNORECASE)
-    _fix_extends_re = re.compile(r'\s+extends\s+', re.IGNORECASE)
+    _spaces_re = re.compile(r'\s+')
     _collapse_properties_space_re = re.compile(r'([:#])\s*{')
     _expand_rules_space_re = re.compile(r'\s*{')
 
@@ -386,6 +305,22 @@ class xCSS(object):
     def __init__(self):
         pass
 
+    def longest_common_prefix(self, seq1, seq2):
+        start = 0
+        common = 0
+        while start < min(len(seq1), len(seq2)):
+            if seq1[start] != seq2[start]:
+                break
+            if seq1[start] == ' ':
+                common = start + 1
+            elif seq1[start] in ('#', ':', '.'):
+                common = start
+            start += 1
+        return common
+    
+    def longest_common_suffix(self, seq1, seq2):
+        return self.longest_common_prefix(seq1[::-1], seq2[::-1])
+
     def locate_blocks(self, str, open='{', close='}', joiner=','):
         """
         Returns all code blocks between `open` and `close` and a proper key
@@ -450,6 +385,111 @@ class xCSS(object):
         losestr = str[lose:]
         yield None, None, losestr
 
+
+    def normalize_selectors(self, _selectors, extra_selectors=None, extra_parents=None):
+        """
+        Normalizes or extends selectors in a string.
+        An optional extra parameter that can be a list of extra selectors to be
+        added to the final normalized selectors string.
+        """
+        # Fixe tabs and spaces in selectors
+        _selectors = self._spaces_re.sub(' ', _selectors)
+
+        if isinstance(extra_selectors, basestring):
+            extra_selectors = extra_selectors.split(',')
+
+        if isinstance(extra_parents, basestring):
+            extra_parents = extra_parents.split('&')
+
+        parents = set()
+        if ' extends ' in _selectors:
+            selectors = set()
+            for key in _selectors.split(','):
+                child, _, parent = key.partition(' extends ')
+                child = child.strip()
+                parent = parent.strip()
+                selectors.add(child)
+                parents.update(s.strip() for s in parent.split('&') if s.strip())
+        else:
+            selectors = set(s.strip() for s in _selectors.split(',') if s.strip())
+        if extra_selectors:
+            selectors.update(s.strip() for s in extra_selectors if s.strip())
+        selectors.discard('')
+        if not selectors:
+            return None
+        if extra_parents:
+            parents.update(s.strip() for s in extra_parents if s.strip())
+        parents.discard('')
+        if parents:
+            return ','.join(sorted(selectors)) + ' extends ' + '&'.join(sorted(parents))
+        return ','.join(sorted(selectors))
+
+
+    def use_vars(self, cont, context=None, options=None):
+        xcss_vars = self.xcss_vars.copy()
+        xcss_vars.update(context or {})
+        vars = xcss_vars.keys()
+        try:
+            remove_vars_re, interpolate_re = self._contexts[tuple(vars)]
+        except KeyError:
+            vars1 = []
+            vars2 = []
+            for var in vars:
+                if var[0] == '$':
+                    vars1.append(re.escape(var))
+                else:
+                    vars2.append(re.escape(var))
+            remove_vars_re = re.compile(r'(?<![-\w])(((' + '|'.join(vars1) + r')\s*[:=]|(' + '|'.join(vars2) + r')\s*=).*?([;}]|$))')
+            interpolate_re = re.compile(r'(?<![-\w])(' + '|'.join(map(re.escape, vars)) + r')(?![-\w])')
+            self._contexts[tuple(vars)] = remove_vars_re, interpolate_re
+
+        # remove variables declarations from the rules
+        cont = self._remove_decls_re.sub('', cont)
+        cont = remove_vars_re.sub('', cont)
+
+        cnt = 0
+        old_cont = None
+        while cont != old_cont and cnt < 5:
+            cnt += 1
+            old_cont = cont
+
+            # interpolate variables:
+            cont = interpolate_re.sub(lambda m: xcss_vars[m.group(0)], cont)
+
+        return cont
+
+
+    def process_properties(self, codestr, context, options, properties=None, scope=''):
+        for p_selectors, p_codestr, lose in self.locate_blocks(codestr):
+            if lose is not None:
+                codestr = lose
+                codes = [ s.strip() for s in codestr.split(';') if s.strip() ]
+                for code in codes:
+                    if code[0] == '@':
+                        code, name = (code.split(None, 1)+[''])[:2]
+                        code = code.strip()
+                        name = name.strip()
+                        options[code] = name
+                    else:
+                        prop, value = (re.split(r'[:=]', code, 1) + [''])[:2]
+                        try:
+                            is_var = (code[len(prop)] == '=')
+                        except IndexError:
+                            is_var = False
+                        prop = prop.strip()
+                        if prop:
+                            value = value.strip()
+                            _prop = scope + prop
+                            if is_var or prop[0] == '$':
+                                if value:
+                                    context[_prop] = value
+                            else:
+                                if properties is not None and value:
+                                    properties[_prop] = value
+            elif p_selectors[-1] == ':':
+                self.process_properties(p_codestr, context, options, properties, scope + p_selectors[:-1] + '-')
+
+
     def compile(self, input_xcss=None):
         # Initialize
         self.rules = []
@@ -495,209 +535,6 @@ class xCSS(object):
 
         return final_cont
 
-    def post_process(self, cont):
-        # short colors:
-        if self.short_colors:
-            cont = self._short_color_re.sub(r'#\1\2\3', cont)
-
-        # color names:
-        if self.reverse_colors:
-            cont = self._reverse_colors_re.sub(lambda m: self._reverse_colors[m.group(0).lower()], cont)
-
-        # zero units out (i.e. 0px or 0em -> 0):
-        cont = self._zero_units_re.sub('0', cont)
-        return cont
-
-    def use_vars(self, cont, context=None, options=None):
-        xcss_vars = self.xcss_vars.copy()
-        xcss_vars.update(context or {})
-        vars = xcss_vars.keys()
-        try:
-            remove_vars_re, interpolate_re = self._contexts[tuple(vars)]
-        except KeyError:
-            vars1 = []
-            vars2 = []
-            for var in vars:
-                if var[0] == '$':
-                    vars1.append(re.escape(var))
-                else:
-                    vars2.append(re.escape(var))
-            remove_vars_re = re.compile(r'(?<![-\w])(((' + '|'.join(vars1) + r')\s*[:=]|(' + '|'.join(vars2) + r')\s*=).*?([;}]|$))')
-            interpolate_re = re.compile(r'(?<![-\w])(' + '|'.join(map(re.escape, vars)) + r')(?![-\w])')
-            self._contexts[tuple(vars)] = remove_vars_re, interpolate_re
-
-        # remove variables declarations from the rules
-        cont = self._remove_decls_re.sub('', cont)
-        cont = remove_vars_re.sub('', cont)
-
-        cnt = 0
-        old_cont = None
-        while cont != old_cont and cnt < 5:
-            cnt += 1
-            old_cont = cont
-
-            # interpolate variables:
-            cont = interpolate_re.sub(lambda m: xcss_vars[m.group(0)], cont)
-
-        return cont
-
-    def do_math(self, content):
-        def calculate(result):
-            _base_str = result.group(0)
-            _expr_str = result.group('expr')
-            _unit_str = result.group('unit')
-            if _expr_str.startswith('url(') or _expr_str.startswith('expression('):
-                return _base_str
-            try:
-                better_expr_str = self._replaces[_base_str]
-            except KeyError:
-                if _expr_str[:2] == '#{' and _expr_str[-1] == '}':
-                    _expr_str = _expr_str[2:-1].strip('[]')
-
-                better_expr_str = self._colors_re.sub(lambda m: self._colors.get(m.group(0), m.group(0)), _expr_str).replace('[', '(').replace(']', ')')
-
-                rgba = None
-                for color in self._color_re.finditer(better_expr_str):
-                    c = color.groupdict()
-                    if c.get('short_R'):
-                        r = int(c.get('short_R')*2, 16)
-                        g = int(c.get('short_G')*2, 16)
-                        b = int(c.get('short_B')*2, 16)
-                        a = 0
-                    elif c.get('long_R'):
-                        r = int(c.get('long_R'), 16)
-                        g = int(c.get('long_G'), 16)
-                        b = int(c.get('long_B'), 16)
-                        a = 0
-                    elif c.get('rgb_R') is not None:
-                        r = int(c.get('rgb_R'))
-                        g = int(c.get('rgb_G'))
-                        b = int(c.get('rgb_B'))
-                        a = 0
-                    else:
-                        r = int(c.get('rgba_R'))
-                        g = int(c.get('rgba_G'))
-                        b = int(c.get('rgba_B'))
-                        a = 255 - int(c.get('rgba_A'))
-                    if c.get('rgb_X') or c.get('rgba_X'):
-                        r = '%02x' % (r * 255 / 100)
-                        g = '%02x' % (g * 255 / 100)
-                        b = '%02x' % (b * 255 / 100)
-                        a = '%02x' % (a * 255 / 100)
-                    else:
-                        r = '%02x' % r
-                        g = '%02x' % g
-                        b = '%02x' % b
-                        a = '%02x' % a
-                    _base_color_str = color.group(0)
-                    if not rgba:
-                        rgba = [
-                            better_expr_str.replace(_base_color_str, '0x'+r),
-                            better_expr_str.replace(_base_color_str, '0x'+g),
-                            better_expr_str.replace(_base_color_str, '0x'+b),
-                            better_expr_str.replace(_base_color_str, '0x'+a),
-                        ]
-                    else:
-                        rgba = [
-                            rgba[0].replace(_base_color_str, '0x'+r),
-                            rgba[1].replace(_base_color_str, '0x'+g),
-                            rgba[2].replace(_base_color_str, '0x'+b),
-                            rgba[3].replace(_base_color_str, '0x'+a),
-                        ]
-
-                if rgba:
-                    try:
-                        r = int(safe_eval(rgba[0])); r = 0 if r < 0 else 255 if r > 255 else r
-                        g = int(safe_eval(rgba[1])); g = 0 if g < 0 else 255 if g > 255 else g
-                        b = int(safe_eval(rgba[2])); b = 0 if b < 0 else 255 if b > 255 else b
-                        a = int(safe_eval(rgba[3])); a = 0 if a < 0 else 255 if a > 255 else a
-                        
-                        if a == 0:
-                            _better_expr_str = '#%02x%02x%02x' % (r, g, b)
-                        else:
-                            _better_expr_str = 'rgba(%d, %d, %d, %d)' % (r, g, b, 255-a)
-                    except NameError:
-                        pass
-                    except ValueError:
-                        pass
-                    except SyntaxError, e:
-                        if self.xcss_opts.get('verbosity', self.verbosity) > 2:
-                            better_expr_str += ' /* ERROR: %s! */' % e
-                    except:
-                        better_expr_str += ' /* ERROR: %s! */' % e
-                    else:
-                        better_expr_str = _better_expr_str
-                else:
-                    try:
-                        global_factor = 1.0
-                        if _unit_str == '%':
-                            global_factor = 100.0
-                        else:
-                            for m in self._full_unit_re.finditer(better_expr_str):
-                                unit = m.group(2)
-                                if unit == '%':
-                                    global_factor = 100.0
-                                    break
-                        
-                        unit_types = set()
-                        my_units = {}
-                        def reunit(m):
-                            value = m.group(1)
-                            unit = m.group(2)
-                            unit = unit and unit.lower()
-                            my_units.setdefault(unit, 0)
-                            my_units[unit] += 1
-                            my_units.setdefault('count', 0)
-                            if my_units['count'] < my_units[unit]:
-                                my_units['count'] = my_units[unit]
-                            if unit == '%' or not unit:
-                                unit_type = None
-                                factor = 1.0
-                            else:
-                                unit_type = self._conv_mapping.get(unit, 'unknown')
-                                factor = self._conv.get(unit_type, {}).get(unit, 1.0)
-                            unit_types.add(unit_type)
-                            return str(float(value) * factor / global_factor)
-                        better_expr_str = self._full_unit_re.sub(reunit, better_expr_str)
-
-                        new_unit = ''
-                        final_unit = _unit_str.lower()
-                        if final_unit in (';', '\t', ' '):
-                            for unit, count in my_units.items():
-                                if unit != 'count' and count == my_units['count']:
-                                    new_unit = unit
-                                    break
-                            final_unit = new_unit = new_unit or ''
-                        if final_unit == '%' or not final_unit:
-                            final_unit_type = None
-                            final_factor = 1.0
-                        elif final_unit:
-                            final_unit_type = self._conv_mapping.get(final_unit, 'unknown')
-                            final_factor = self._conv.get(final_unit_type, {}).get(final_unit, 1.0)
-                        unit_types.add(final_unit_type)
-                        unit_types.discard(None)
-                        _better_expr_str = self._unit_re.sub('', better_expr_str)
-                        num = str('%0.04f' % round(safe_eval(_better_expr_str) * global_factor / final_factor)).rstrip('0').rstrip('.')
-                        _better_expr_str = '%s%s' % (num, new_unit)
-                        if len(unit_types) > 1:
-                            _better_expr_str += ' /* ERROR: units mismatch: %s! */' % ' vs. '.join(unit_types)
-                    except NameError:
-                        pass
-                    except ValueError:
-                        pass
-                    except SyntaxError, e:
-                        if self.xcss_opts.get('verbosity', self.verbosity) > 2:
-                            better_expr_str += ' /* ERROR: %s! */' % e
-                    except Exception, e:
-                        better_expr_str += ' /* ERROR: %s! */' % e
-                    else:
-                        better_expr_str = _better_expr_str
-                self._replaces[_base_str] = better_expr_str
-            return better_expr_str + _unit_str
-        #print >>sys.stderr, self._expr_re.findall(content)
-        content = self._expr_re.sub(calculate, content)
-        return content
-
     def parse_xcss_string(self, fileid, str):
         # protects content: "..." strings
         str = self._reverse_default_xcss_vars_re.sub(lambda m: m.group(0) + self._reverse_default_xcss_vars.get(m.group(2)) + m.group(3), str)
@@ -712,8 +549,6 @@ class xCSS(object):
         str = self._expand_rules_space_re.sub(' {', str)
         # collapse the space in properties blocks
         str = self._collapse_properties_space_re.sub(r'\1{', str)
-        # Fixe tabs and spaces in ' extends '
-        str = self._fix_extends_re.sub(' extends ', str)
 
         my_rules = []
         context = {}
@@ -807,208 +642,6 @@ class xCSS(object):
             rule[OPTIONS] = options.copy()
             rule[CODESTR] = self._includes_re.sub(expand_includes, rule[CODESTR])
 
-    def process_properties(self, codestr, context, options, properties=None, scope=''):
-        for p_selectors, p_codestr, lose in self.locate_blocks(codestr):
-            if lose is not None:
-                codestr = lose
-                codes = [ s.strip() for s in codestr.split(';') if s.strip() ]
-                for code in codes:
-                    prop, value = (re.split(r'[:=]', code, 1) + [''])[:2]
-                    try:
-                        is_var = (code[len(prop)] == '=')
-                    except IndexError:
-                        is_var = False
-
-                    prop = prop.strip()
-                    if prop:
-                        value = value.strip()
-                        _prop = scope + prop
-                        if prop[0] == '@':
-                            prop, name = (prop.split(None, 1)+[''])[:2]
-                            prop = prop.strip()
-                            name = name.strip()
-                            options[prop + ' ' + name] = value
-                        elif is_var or prop[0] == '$':
-                            if value:
-                                context[_prop] = value
-                        else:
-                            if properties is not None and value:
-                                properties[_prop] = value
-            elif p_selectors[-1] == ':':
-                self.process_properties(p_codestr, context, options, properties, scope + p_selectors[:-1] + '-')
-
-    def parse_properties(self):
-        # build final properties:
-        for _selectors, rules in self.parts.items():
-            for rule in rules:
-                fileid, position, codestr, deps, context, options, selectors, properties = rule
-                if position is not None and codestr and properties is None:
-                    assert selectors is None, "Rule body is repeated for different selectors!"
-                    rule[SELECTORS] = _selectors
-                    rule[PROPERTIES] = properties = rule[PROPERTIES] or {}
-                    rule[CONTEXT] = context = rule[CONTEXT] or {}
-                    rule[OPTIONS] = context = rule[OPTIONS] or {}
-                    self.process_properties(codestr, context, options, properties)
-
-    def manage_order(self):
-        # order rules according with their dependencies
-        for rule in self.rules:
-            if rule[POSITION] is not None:
-                rule[DEPS].add(rule[POSITION]+1)
-                # This moves the rules just above the topmost dependency during the sorted() below:
-                rule[POSITION] = min(rule[DEPS])
-        self.rules = sorted(self.rules, key=lambda o: o[POSITION])
-
-        self.css_files = []
-        self._rules = {}
-        css_files = set()
-        old_fileid = None
-        for rule in self.rules:
-            fileid, position, codestr, deps, context, options, selectors, properties = rule
-            self._rules.setdefault(fileid, [])
-            self._rules[fileid].append(rule)
-            if position is not None and properties:
-                if old_fileid != fileid:
-                    old_fileid = fileid
-                    if fileid not in css_files:
-                        css_files.add(fileid)
-                        self.css_files.append(fileid)
-
-    def create_css(self, fileid=None):
-        # generate the final CSS string
-        result = ''
-        if fileid:
-            rules = self._rules.get(fileid) or []
-        else:
-            rules = self.rules
-
-        for rule in rules:
-            fileid, position, codestr, deps, context, options, selectors, properties = rule
-            #print >>sys.stderr, fileid, position, context, options, selectors, properties
-            if position is not None and properties:
-                # feel free to modifie the indentations the way you like it
-                result += ',\n'.join(selectors.split(',')) + ' {\n'
-                if options.get('verbosity', self.verbosity) > 0:
-                    result += '\t/* file: ' + fileid + ' */\n'
-                    if context:
-                        result += '\t/* vars:\n'
-                        for k, v in context.items():
-                            result += '\t\t' + k + ' = ' + v + ';\n'
-                        result += '\t*/\n'
-                for prop, value in properties.items():
-                    result += '\t' + prop + ': ' + value + ';\n'
-                result += '}\n'
-        return result
-
-    def search_for_parent(self, parent, c_selectors, c_rules):
-        parent_found = None
-        for p_selectors, p_rules in self.parts.items():
-            _p_selectors, _, _ = p_selectors.partition(' extends ')
-            _p_selectors = _p_selectors.split(',')
-            new_selectors = set()
-            # finds all the parent selectors and parent selectors with another
-            # bind selectors behind. For example, if `.specialClass extends .baseClass`,
-            # and there is a `.baseClass` selector, the extension should create
-            # `.specialClass` for that rule, but if there's also a `.baseClass a`
-            # it also should create `.specialClass a`
-            for p_selector in _p_selectors:
-                if parent in p_selector:
-                    # get the new child selector to add (same as the parent selector but with the child name)
-                    # since selectors can be together, separated with # or . (i.e. something.parent) check that too:
-                    for c_selector in c_selectors.split(','):
-                        new_selectors.add(re.sub(parent[0] not in ('#', '.') and r'(?<!\w|-)' or '' + parent + r'(?!\w|-)', c_selector, p_selector))
-            if new_selectors:
-                new_selectors = self.normalize_selectors(p_selectors, new_selectors)
-                # rename node:
-                if new_selectors != p_selectors:
-                    self.parts.setdefault(new_selectors, [])
-                    self.parts[new_selectors].extend(p_rules)
-                    del self.parts[p_selectors]
-
-                # save child dependencies:
-                for c_rule in c_rules or []:
-                    for p_rule in p_rules:
-                        p_rule[DEPS].add(c_rule[POSITION]) # position is the "index" of the object
-
-                # add parent:
-                parent_found = parent_found or []
-                parent_found.extend(p_rules)
-
-        return parent_found
-
-    def manage_multiple_extends(self, parts):
-        # To be able to manage multiple extends, you need to
-        # destroy the actual node and create many nodes that have
-        # mono extend. The first one gets all the css rules
-        for _selectors, rules in parts.items():
-            if ' extends ' in _selectors:
-                selectors, _, parent = _selectors.partition(' extends ')
-                parents = parent.split('&')
-                del parts[_selectors]
-                for parent in parents:
-                    new_selectors = selectors + ' extends ' + parent
-                    parts.setdefault(new_selectors, [])
-                    parts[new_selectors].extend(rules)
-                    rules = [] # further rules extending other parents will be empty
-
-    def parse_extends(self):
-        self.manage_multiple_extends(self.parts)
-        for _selectors, rules in self.parts.items():
-            selectors, _, parent = _selectors.partition(' extends ')
-            if parent:
-                self.parts.setdefault(selectors, [])
-                self.parts[selectors].extend(rules)
-                if _selectors in self.parts:
-                    # It might be that search_for_parent or previous iterations
-                    # already have removed the selectors...
-                    del self.parts[_selectors]
-                parents = self.search_for_parent(parent, selectors, rules)
-
-                assert parents is not None, "Parent not found: %s (%s)" % (parent, selectors)
-
-                # from the parent, copy the context and the options:
-                new_context = {}
-                new_options = {}
-                for parent in parents:
-                    new_context.update(parent[CONTEXT])
-                    new_options.update(parent[OPTIONS])
-                for rule in rules:
-                    _new_context = new_context.copy()
-                    _new_context.update(rule[CONTEXT])
-                    rule[CONTEXT] = _new_context
-                    _new_options = new_options.copy()
-                    _new_options.update(rule[OPTIONS])
-                    rule[OPTIONS] = _new_options
-
-    def normalize_selectors(self, _selectors, selector=None):
-        if isinstance(selector, basestring):
-            selector = set([selector])
-        if ' extends ' in _selectors:
-            parents = set()
-            selectors = set()
-            for key in _selectors.split(','):
-                child, _, parent = key.partition(' extends ')
-                child = child.strip()
-                parent = parent.strip()
-                selectors.add(child)
-                parents.update(s.strip() for s in parent.split('&') if s.strip())
-            if selector:
-                selectors.update(selector)
-            selectors.discard('')
-            if not selectors:
-                return None
-            parents.discard('')
-            if parents:
-                return ','.join(sorted(selectors)) + ' extends ' + '&'.join(sorted(parents))
-            return ','.join(sorted(selectors))
-        else:
-            selectors = set(s.strip() for s in _selectors.split(',') if s.strip())
-            if selector:
-                selectors.update(selector)
-            selectors.discard('')
-            if not selectors:
-                return None
-            return ','.join(sorted(selectors))
 
     def parse_children(self):
         cnt = 0
@@ -1044,14 +677,10 @@ class xCSS(object):
                         options = dict(filter(lambda x: not x[0].startswith('@extend '), options.items())) # clean options
                         self.process_properties(codestr, context, options)
                         rule[CODESTR] = self.use_vars(codestr, context, options)
-                        for o in options:
-                            if o.startswith('@extend '):
-                                parents = o[8:].replace(',', '&')
-                                if ' extends ' in new_selectors:
-                                    new_selectors += '&'+parents
-                                else:
-                                    new_selectors += ' extends ' + parents
-                                new_selectors = self.normalize_selectors(new_selectors)
+                        parents = options.get('@extend')
+                        if parents:
+                            parents = parents.replace(',', '&') # @extend can come with comma separated selectors...
+                            new_selectors = self.normalize_selectors(new_selectors, extra_parents=parents)
                     # rename selectors (if interpolated)
                     if new_selectors != _selectors:
                         del self.parts[_selectors]
@@ -1085,8 +714,8 @@ class xCSS(object):
                     for p_selector in p_selectors:
                         if c_selector == self.construct:
                             better_selectors.add(p_selector)
-                        elif c_selector[0] == '&': # Parent References (SASS)
-                            better_selectors.add(p_selector + c_selector[1:])
+                        elif '&' in c_selector: # Parent References (SASS)
+                            better_selectors.add(c_selector.replace('&', p_selector))
                         else:
                             better_selectors.add(p_selector + ' ' + c_selector)
                 better_selectors = ','.join(sorted(better_selectors))
@@ -1119,6 +748,508 @@ class xCSS(object):
                 rule[CONTEXT] = context.copy()
                 rule[OPTIONS] = options.copy()
 
+    def link_with_parents(self, parent, c_selectors, c_rules):
+        """
+        Link with a parent for the current child rule.
+        If parents found, returns a list of parent rules to the child
+        """
+        parent_found = None
+        for p_selectors, p_rules in self.parts.items():
+            _p_selectors, _, _ = p_selectors.partition(' extends ')
+            _p_selectors = _p_selectors.split(',')
+            
+            new_selectors = set()
+            found = False
+
+            # Finds all the parent selectors and parent selectors with another
+            # bind selectors behind. For example, if `.specialClass extends .baseClass`,
+            # and there is a `.baseClass` selector, the extension should create
+            # `.specialClass` for that rule, but if there's also a `.baseClass a`
+            # it also should create `.specialClass a`
+            for p_selector in _p_selectors:
+                if parent in p_selector:
+                    # get the new child selector to add (same as the parent selector but with the child name)
+                    # since selectors can be together, separated with # or . (i.e. something.parent) check that too:
+                    for c_selector in c_selectors.split(','):
+                        # Get whatever is different between the two selectors:
+                        lcp = self.longest_common_prefix(c_selector, p_selector)
+                        if lcp: c_selector = c_selector[lcp:]
+                        lcs = self.longest_common_suffix(c_selector, p_selector)
+                        if lcs: c_selector = c_selector[:-lcs]
+                        # Get the new selectors:
+                        prev_symbol = r'(?<![-\w])' if parent[0] not in ('#', '.', ':') else ''
+                        post_symbol = r'(?![-\w])'
+                        new_parent = re.sub(prev_symbol + parent + post_symbol, c_selector, p_selector)
+                        new_selectors.add(new_parent)
+                        found = True
+
+            if found:
+                # add parent:
+                parent_found = parent_found or []
+                parent_found.extend(p_rules)
+
+            if new_selectors:
+                new_selectors = self.normalize_selectors(p_selectors, new_selectors)
+                # rename node:
+                if new_selectors != p_selectors:
+                    del self.parts[p_selectors]
+                    self.parts.setdefault(new_selectors, [])
+                    self.parts[new_selectors].extend(p_rules)
+
+                # save child dependencies:
+                for c_rule in c_rules or []:
+                    for p_rule in p_rules:
+                        p_rule[DEPS].add(c_rule[POSITION]) # position is the "index" of the object
+
+        return parent_found
+
+    def parse_extends(self):
+        """
+        For each part, create the inheritance parts from the ' extends '
+        """
+        # To be able to manage multiple extends, you need to
+        # destroy the actual node and create many nodes that have
+        # mono extend. The first one gets all the css rules
+        for _selectors, rules in self.parts.items():
+            if ' extends ' in _selectors:
+                selectors, _, parent = _selectors.partition(' extends ')
+                parents = parent.split('&')
+                del self.parts[_selectors]
+                for parent in parents:
+                    new_selectors = selectors + ' extends ' + parent
+                    self.parts.setdefault(new_selectors, [])
+                    self.parts[new_selectors].extend(rules)
+                    rules = [] # further rules extending other parents will be empty
+
+        for _selectors, rules in self.parts.items():
+            selectors, _, parent = _selectors.partition(' extends ')
+            if parent:
+                if _selectors in self.parts:
+                    # It might be that link_with_parents or previous iterations
+                    # already have removed the selectors... !!??
+                    del self.parts[_selectors]
+                self.parts.setdefault(selectors, [])
+                self.parts[selectors].extend(rules)
+
+                parents = self.link_with_parents(parent, selectors, rules)
+
+                assert parents is not None, "Parent not found: %s (%s)" % (parent, selectors)
+
+                # from the parent, inherit the context and the options:
+                new_context = {}
+                new_options = {}
+                for parent in parents:
+                    new_context.update(parent[CONTEXT])
+                    new_options.update(parent[OPTIONS])
+                for rule in rules:
+                    _new_context = new_context.copy()
+                    _new_context.update(rule[CONTEXT])
+                    rule[CONTEXT] = _new_context
+                    _new_options = new_options.copy()
+                    _new_options.update(rule[OPTIONS])
+                    rule[OPTIONS] = _new_options
+
+
+    def manage_order(self):
+        # order rules according with their dependencies
+        for rule in self.rules:
+            if rule[POSITION] is not None:
+                rule[DEPS].add(rule[POSITION]+1)
+                # This moves the rules just above the topmost dependency during the sorted() below:
+                rule[POSITION] = min(rule[DEPS])
+        self.rules = sorted(self.rules, key=lambda o: o[POSITION])
+
+        self.css_files = []
+        self._rules = {}
+        css_files = set()
+        old_fileid = None
+        for rule in self.rules:
+            fileid, position, codestr, deps, context, options, selectors, properties = rule
+            self._rules.setdefault(fileid, [])
+            self._rules[fileid].append(rule)
+            if position is not None and properties:
+                if old_fileid != fileid:
+                    old_fileid = fileid
+                    if fileid not in css_files:
+                        css_files.add(fileid)
+                        self.css_files.append(fileid)
+
+
+    def parse_properties(self):
+        # build final properties:
+        for _selectors, rules in self.parts.items():
+            for rule in rules:
+                fileid, position, codestr, deps, context, options, selectors, properties = rule
+                if position is not None and codestr and properties is None:
+                    assert selectors is None, "Rule body is repeated for different selectors!"
+                    rule[SELECTORS] = _selectors
+                    rule[PROPERTIES] = properties = rule[PROPERTIES] or SortedDict()
+                    rule[CONTEXT] = context = rule[CONTEXT] or {}
+                    rule[OPTIONS] = context = rule[OPTIONS] or {}
+                    self.process_properties(codestr, context, options, properties)
+
+
+    def create_css(self, fileid=None):
+        """
+        Generate the final CSS string
+        """
+        result = ''
+        if fileid:
+            rules = self._rules.get(fileid) or []
+        else:
+            rules = self.rules
+
+        for rule in rules:
+            fileid, position, codestr, deps, context, options, selectors, properties = rule
+            #print >>sys.stderr, fileid, position, context, options, selectors, properties
+            if position is not None and properties:
+                # feel free to modifie the indentations the way you like it
+                result += ',\n'.join(selectors.split(',')) + ' {\n'
+                if options.get('verbosity', self.verbosity) > 0:
+                    result += '\t/* file: ' + fileid + ' */\n'
+                    if context:
+                        result += '\t/* vars:\n'
+                        for k, v in context.items():
+                            result += '\t\t' + k + ' = ' + v + ';\n'
+                        result += '\t*/\n'
+                for prop, value in properties.items():
+                    result += '\t' + prop + ': ' + value + ';\n'
+                result += '}\n'
+        return result
+
+
+    def do_math(self, content):
+        def calculate(result):
+            _base_str = result.group(0)
+
+            try:
+                better_expr_str = self._replaces[_base_str]
+            except KeyError:
+                if _base_str[:2] == '#{' and _base_str[-1] == '}':
+                    _base_str = _base_str[2:-1]
+
+                better_expr_str = self._colors_re.sub(lambda m: _colors.get(m.group(0), m.group(0)), _base_str).replace('[', '(').replace(']', ')')
+                try:
+                    better_expr_str = eval_expr(better_expr_str)
+                except:
+                    pass
+
+                self._replaces[_base_str] = better_expr_str
+            return better_expr_str
+        #print >>sys.stderr, self._expr_re.findall(content)
+        content = self._expr_re.sub(calculate, content)
+        return content
+
+    def post_process(self, cont):
+        # short colors:
+        if self.short_colors:
+            cont = self._short_color_re.sub(r'#\1\2\3', cont)
+
+        # color names:
+        if self.reverse_colors:
+            cont = self._reverse_colors_re.sub(lambda m: self._reverse_colors[m.group(0).lower()], cont)
+
+        # zero units out (i.e. 0px or 0em -> 0):
+        cont = self._zero_units_re.sub('0', cont)
+        return cont
+
+
+from pyparsing import *
+import math
+import operator
+
+exprStack = []
+
+def pushFirst( strg, loc, toks ):
+    exprStack.append( toks[0] )
+
+def pushQuoted( strg, loc, toks ):
+    exprStack.append( u'"%s"' % toks[0] )
+
+def pushString( strg, loc, toks ):
+    exprStack.append( u"'%s'" % toks[0] )
+
+def pushUnifier( strg, loc, toks ):
+    if toks and toks[0] in _units: 
+        exprStack.append( u"unary %s" % toks[0] )
+
+def pushUMinus( strg, loc, toks ):
+    if toks and toks[0]=='-': 
+        exprStack.append( 'unary -' )
+
+bnf = None
+def BNF():
+    global bnf
+    if not bnf:
+        expr = Forward()
+
+        point  = Literal( '.' )
+        comma  = Literal( ',' ).suppress()
+        plus   = Literal( '+' )
+        minus  = Literal( '-' )
+        mult   = Literal( '*' )
+        div    = Literal( '/' )
+        lpar   = Literal( '(' ).suppress()
+        rpar   = Literal( ')' ).suppress()
+        expop  = Literal( '^' )
+        
+        units = None
+        for u in _units:
+            if not units:
+                units = Literal( u )
+            else:
+                units |= Literal( u )
+        unit = Combine( units )
+
+        addop  = plus | minus
+        multop = mult | div
+        ident  = Word(alphas, alphas+nums+'_$')
+        string = QuotedString('"') | QuotedString("'")
+        funct  = Combine(ident + lpar + expr.suppress() + ZeroOrMore(comma + expr.suppress()) + rpar)
+        color  = Combine(Literal( '#' ) + Word(hexnums, exact=8) | # #RRGGBBAA
+                         Literal( '#' ) + Word(hexnums, exact=6) | # #RRGGBB
+                         Literal( '#' ) + Word(hexnums, exact=4) | # #RGBA
+                         Literal( '#' ) + Word(hexnums, exact=3)   # #RGB
+        )
+        fnumber = Combine(
+            Word( '+-'+nums, nums ) + Optional( point + Optional( Word( nums ) ) ) + Optional( unit ) |
+            point + Word( nums ) + Optional( Literal( '%' ) )
+        )
+        
+        atom = (
+            Optional('-') +
+            ( fnumber | funct | color ).setParseAction( pushFirst ) |
+            ( string ).setParseAction( pushQuoted ) |
+            ( ident  ).setParseAction( pushString ) |
+            ( lpar + expr.suppress() + rpar + Optional( unit )).setParseAction(pushUnifier)
+        ).setParseAction(pushUMinus)
+        
+        # by defining exponentiation as 'atom [ ^ factor ]...' instead of 'atom [ ^ atom ]...', we get right-to-left exponents, instead of left-to-righ
+        # that is, 2^3^2 = 2^(3^2), not (2^3)^2.
+        factor = Forward()
+        factor << atom + ZeroOrMore( ( expop + factor ).setParseAction( pushFirst ) )
+        
+        term = factor + ZeroOrMore( ( multop + factor ).setParseAction( pushFirst ) )
+        expr << term + ZeroOrMore( ( addop + term ).setParseAction( pushFirst ) )
+        bnf = expr
+    return bnf
+
+# map operator symbols to corresponding arithmetic operations
+hex2rgba = {
+    9: lambda c: (int(c[1:3], 16), int(c[3:5], 16), int(c[5:7], 16), int(c[7:9], 16)),
+    7: lambda c: (int(c[1:3], 16), int(c[3:5], 16), int(c[5:7], 16), 255),
+    5: lambda c: (int(c[1]*2, 16), int(c[2]*2, 16), int(c[3]*2, 16), int(c[4]*2, 16)),
+    4: lambda c: (int(c[1]*2, 16), int(c[2]*2, 16), int(c[3]*2, 16), 255),
+}
+def _rgbhex(hex):
+    return (hex, None, hex2rgba[len(hex)](hex), {'#':1})
+def _rgb(_r, _g, _b):
+    r = _r[1]
+    g = _g[1]
+    b = _b[1]
+    rp = 1 if '%' in _r[3] else 0
+    gp = 1 if '%' in _g[3] else 0
+    bp = 1 if '%' in _b[3] else 0
+    r = r * 255 if rp else 0 if r < 0 else 255 if r > 255 else r
+    g = g * 255 if rp else 0 if g < 0 else 255 if g > 255 else g
+    b = b * 255 if rp else 0 if b < 0 else 255 if b > 255 else b
+    d = { 'rgb': 1 }
+    p = rp + gp + bp
+    if p: d['%'] = p
+    return ('#%02x%02x%02x' % (r,g,b), None, (r, g, b, 255), )
+def _rgba(_r, _g, _b, _a):
+    if _a[1] == 255:
+        return _rgb(_r, _g, _b)
+    r = _r[1]
+    g = _g[1]
+    b = _b[1]
+    a = _a[1]
+    rp = 1 if '%' in _r[3] else 0
+    gp = 1 if '%' in _g[3] else 0
+    bp = 1 if '%' in _b[3] else 0
+    ap = 1 if '%' in _a[3] else 0
+    p = (r > 0 and r <= 1 and g > 0 and g <= 1 and b > 0 and b <= 1 and a > 0 and a <= 1)
+    r = r * 255 if rp else 0 if r < 0 else 255 if r > 255 else r
+    g = g * 255 if gp else 0 if g < 0 else 255 if g > 255 else g
+    b = b * 255 if bp else 0 if b < 0 else 255 if b > 255 else b
+    a = a * 255 if ap else 0 if a < 0 else 255 if a > 255 else a
+    d = { 'rgba': 1 }
+    p = rp + gp + bp
+    if p: d['%'] = p
+    return ('rgba(%s, %s, %s, %s)' % (float2str(r), float2str(g), float2str(b), float2str(a)), None, (r, g, b, a), d)
+def _float(val):
+    _val = val[1]
+    val[3].pop(None, None)
+    units = sorted(val[3], key=val[3].get, reverse=True)
+    if units:
+        units_type = set()
+        for unit in units:
+            units_type.add(_conv_mapping.get(unit))
+        unit = units[0]
+        unit_type = _conv_mapping.get(unit)
+        factor = _conv.get(unit_type, {}).get(unit, 1)
+        assert len(units_type) <= 1, "Units mismatch"
+        _val /= factor
+        _val = float2str(_val)
+        
+        if unit in _units:
+            _val += unit
+    _val = float2str(_val)
+    return (_val, val[1], val[2], val[3])
+
+def _ops(op):
+    _op = op
+    op = {
+        '+' : operator.add,
+        '-' : operator.sub,
+        '*' : operator.mul,
+        '/' : operator.truediv,
+        '^' : operator.pow,
+    }[op]
+    def __ops(_a, _b):
+        a = _a[1]
+        b = _b[1]
+        if a is not None and b is not None:
+            val = op(a, b)
+            d = _a[3].copy()
+            for k, v in _b[3].items():
+                d.setdefault(k, 0)
+                d[k] += 1
+            
+            return _float(('', val, _a[2], d))
+
+        a_str = _a[0]
+        b_str = _b[0]
+        a_rgba = _a[2]
+        b_rgba = _b[2]
+
+        quoting = (a_str[0] == '"' or b_str[0] == '"')
+        if a_str[0] == '"' or a_str[0] == "'": a_str = a_str[1:-1]
+        if b_str[0] == '"' or b_str[0] == "'": a_str = b_str[1:-1]
+        
+        if (a_rgba is not None and b is not None or
+            b_rgba is not None and a is not None or
+           a_rgba is not None and b_rgba is not None):
+            __rgba = [0, 0, 0, 0]
+            for c in range(4):
+                __a = a_rgba[c] if a_rgba is not None else a if c < 3 else None
+                __b = b_rgba[c] if b_rgba is not None else b if c < 3 else None
+                if c == 3:
+                    __rgba[c] = __a if __b is None else __b if __a is None else (__a + __b) / 2
+                else:
+                    __rgba[c] = op(__a, __b)
+            final = _rgba(('',__rgba[0],None,{}), ('',__rgba[1],None,{}), ('',__rgba[2],None,{}), ('',__rgba[3],None,{}))
+        elif quoting:
+            if _op == '*':
+                val = u'"%s"' % op(int(a) if a is not None else a_str, int(b) if b is not None else b_str)
+            else:
+                val = u'"%s"' % op(a_str, b_str)
+            final = (val, None, None, None, {})
+        else:
+            val = u"'%s%s%s'" % (a_str, _op, b_str)
+            final = (val, None, None, None, {})
+
+        return final
+    return __ops
+opn = {
+    '+' : _ops('+'),
+    '-' : _ops('-'),
+    '*' : _ops('*'),
+    '/' : _ops('/'),
+    '^' : _ops('^'),
+}
+def trunc(v):
+    return float(int(v))
+
+def _func(fn):
+    def _func(_val):
+        if _val[1] is not None:
+            val = fn(_val[1])
+        else:
+            val = 0.0
+        return (float2str(val), val, None, _val[3])
+fncs = {
+    'opacify': (2, lambda c,v: c),
+    'transparentize': (2, lambda c,v: c),
+    'hsl': (3, lambda h,s,l: h),
+    'hsla': (4, lambda h,s,l,a: h),
+    'rgb': (3, _rgb),
+    'rgba': (4, _rgba),
+
+    'sin' : (1, _func(math.sin)),
+    'cos' : (1, _func(math.cos)),
+    'tan' : (1, _func(math.tan)),
+    'abs' : (1, _func(abs)),
+    'trunc' : (1, _func(trunc)),
+    'round' : (1, _func(round)),
+}
+def evaluateStack( s ):
+    op = s.pop()
+    if op.startswith('unary '):
+        op = op[6:]
+        if op == '-':
+            op = evaluateStack( s )
+            if op[1] is not None:
+                val = -op[1]
+                return (float2str(val), val, op[2], op[3])
+            elif op[2] is None:
+                if op[0][0] != '"':
+                    val = '-' + op[0]
+                else:
+                    val = op[0]
+                return (val, None, op[2], op[3])
+            return op
+        else:
+            val = evaluateStack( s )
+            if val[1]:
+                val[3].clear()
+                val[3][op] = 1
+                val = _float(val)
+                return val
+            return val
+    elif op in '+-*/^':
+        op2 = evaluateStack( s )
+        op1 = evaluateStack( s )
+        return opn[op]( op1, op2 )
+    elif op in fncs:
+        args, fn = fncs[op]
+        ops = []
+        while args:
+            args -= 1
+            op = evaluateStack( s )
+            ops.insert(0, op)
+        return fn( *ops )
+    elif op[0] == '#':
+        return _rgbhex(op)
+    elif op[0] in ( '"', "'" ):
+        return (op, None, None, {})
+    else:
+        unit = None
+        for i in range(len(op)):
+            if op[-i-1].isdigit():
+                if i:
+                    unit = op[-i:]
+                    op = op[:-i]
+                break
+        val = float(op)
+        if unit:
+            unit_type = _conv_mapping.get(unit)
+            val *= _conv.get(unit_type, {}).get(unit, 1)
+            return (op+unit, val, None, {unit:1})
+        return (op, val, None, {})
+
+def eval_expr(expr):
+    global exprStack
+    exprStack = []
+    #print '>>',expr,'<<'
+    results = BNF().parseString( expr, parseAll=True )
+    val = evaluateStack( exprStack[:] )
+    val = val[0]
+    if val[0] == "'":
+        val = val[1:-1]
+    #print '--',val,'--'
+    return val
+
 
 __doc__ += """
 >>> css = xCSS()
@@ -1237,7 +1368,6 @@ EXTENDING OBJECTS
 http://xcss.antpaw.org/docs/syntax/extends
 
 >>> print css.compile('''
-...
 ... .basicClass {
 ...     padding: 20px;
 ...     background-color: #FF0000;
@@ -1586,19 +1716,19 @@ http://sass-lang.com/tutorial.html
 ... #sidebar { @include rounded(left, 8px); }
 ... ''') #doctest: +NORMALIZE_WHITESPACE
 #navbar li {
-	border-(top)-radius: 10px;
-	-moz-border-radius-(top): 10px;
-	-webkit-border-(top)-radius: 10px;
+	border-top-radius: 10px;
+	-moz-border-radius-top: 10px;
+	-webkit-border-top-radius: 10px;
 }
 #footer {
-	border-(top)-radius: 5px;
-	-moz-border-radius-(top): 5px;
-	-webkit-border-(top)-radius: 5px;
+	border-top-radius: 5px;
+	-moz-border-radius-top: 5px;
+	-webkit-border-top-radius: 5px;
 }
 #sidebar {
-	border-(left)-radius: 8px;
-	-moz-border-radius-(left): 8px;
-	-webkit-border-(left)-radius: 8px;
+	border-left-radius: 8px;
+	-moz-border-radius-left: 8px;
+	-webkit-border-left-radius: 8px;
 }
 
 
@@ -1648,8 +1778,7 @@ Multiple Extends
 ...   background-color: #ff0;
 ... }
 ... .seriousError {
-...   @extend .error;
-...   @extend .attention;
+...   @extend .error, .attention;
 ...   border-width: 3px;
 ... }
 ... ''') #doctest: +NORMALIZE_WHITESPACE
@@ -1735,73 +1864,6 @@ http://groups.google.com/group/xcss/browse_thread/thread/04faafb4ef178984#
 }
 
 
-TESTS
---------------------------------------------------------------------------------
-
->>> print css.compile('''
-... .coloredClass {
-...     $mycolor: green;
-...     padding: 20px;
-...     background-color: $mycolor;
-... }
-... ''') #doctest: +NORMALIZE_WHITESPACE
-    .coloredClass {
-    	padding: 20px;
-    	background-color: green;
-    }
-
-
->>> css.xcss_files = {}
->>> css.xcss_files['first.css'] = '''
-... .specialClass extends .basicClass {
-...     padding: 10px;
-...     font-size: 14px;
-... }
-... '''
->>> css.xcss_files['second.css'] = '''
-... .basicClass {
-...     padding: 20px;
-...     background-color: #FF0000;
-... }
-... '''
->>> print css.compile() #doctest: +NORMALIZE_WHITESPACE
-/* Generated frm: second.css */
-.basicClass,
-.specialClass {
-    padding: 20px;
-    background-color: red;
-}
-/* Generated frm: first.css */
-.specialClass {
-    padding: 10px;
-    font-size: 14px;
-}
-
-
->>> print css.compile('''
-... .mod {
-... 	margin: 10px;
-... }
-... .mod h1 {
-... 	font-size: 40px;
-... }
-... .cleanBox h1 extends .mod {
-... 	font-size: 60px;
-... }
-... ''') #doctest: +NORMALIZE_WHITESPACE
-.cleanBox h1,
-.mod {
-	margin: 10px;
-}
-.cleanBox h1,
-.mod h1 {
-	font-size: 40px;
-}
-.cleanBox h1 {
-	font-size: 60px;
-}
-
-
 ERRORS
 --------------------------------------------------------------------------------
 
@@ -1859,7 +1921,6 @@ http://groups.google.com/group/xcss/browse_thread/thread/540f8ad0771c053b#
 	some: props;
 }
 
-
 http://groups.google.com/group/xcss/browse_thread/thread/b5757c24586c1519#
 >>> print css.compile('''
 ... .mod {
@@ -1896,29 +1957,82 @@ http://groups.google.com/group/xcss/browse_thread/thread/b5757c24586c1519#
 	font-size: 60px;
 }
 
-"""
-"""
 
+TESTS
+--------------------------------------------------------------------------------
 
 >>> print css.compile('''
-... .hoverlink {@extend a:hover}
-... a:hover {text-decoration: underline}
+... .coloredClass {
+...     $mycolor: green;
+...     padding: 20px;
+...     background-color: $mycolor;
+... }
 ... ''') #doctest: +NORMALIZE_WHITESPACE
-.hoverlink,
-a:hover {
-	text-decoration: underline;
+    .coloredClass {
+    	padding: 20px;
+    	background-color: green;
+    }
+
+
+>>> css.xcss_files = SortedDict()
+>>> css.xcss_files['first.css'] = '''
+... .specialClass extends .basicClass {
+...     padding: 10px;
+...     font-size: 14px;
+... }
+... '''
+>>> css.xcss_files['second.css'] = '''
+... .basicClass {
+...     padding: 20px;
+...     background-color: #FF0000;
+... }
+... '''
+>>> print css.compile() #doctest: +NORMALIZE_WHITESPACE
+/* Generated frm: second.css */
+.basicClass,
+.specialClass {
+    padding: 20px;
+    background-color: red;
+}
+/* Generated frm: first.css */
+.specialClass {
+    padding: 10px;
+    font-size: 14px;
 }
 
+
 >>> print css.compile('''
-... .hoverlink {@extend a:hover}
-... .comment a.user:hover {font-weight: bold}
+... a, button {
+...     color: blue;
+...     &:hover, .some & {
+...         text-decoration: underline;
+...     }
+... }
 ... ''') #doctest: +NORMALIZE_WHITESPACE
-.comment a.user:hover,
-.comment .hoverlink.user {
-	font-weight: bold;
+a,
+button {
+    color: #00f;
+}
+.some a,
+.some button,
+a:hover,
+button:hover {
+    text-decoration: underline;
 }
 
 
+All styles defined for a:hover are also applied to .hoverlink:
+>>> print css.compile('''
+... a:hover { text-decoration: underline }
+... .hoverlink { @extend a:hover }
+... ''') #doctest: +NORMALIZE_WHITESPACE
+.hoverlink,
+a:hover {
+	text-decoration: underline;
+}
+
+
+http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html
 >>> print css.compile('''
 ... #fake-links .link {@extend a}
 ... 
@@ -1927,19 +2041,66 @@ a:hover {
 ...   &:hover {text-decoration: underline}
 ... }
 ... ''') #doctest: +NORMALIZE_WHITESPACE
-#fake-links .linka,
+#fake-links .link,
 a {
 	color: #00f;
 }
-#fake-links .link:hover ,
+#fake-links .link:hover,
 a:hover {
 	text-decoration: underline;
 }
 
 
 >>> print css.compile('''
-... #admin .tabbar a {font-weight: bold}
-... #demo .overview .fakelink {@extend a}
+... .mod {
+... 	margin: 10px;
+... }
+... .mod h1 {
+... 	font-size: 40px;
+... }
+... .cleanBox h1 extends .mod {
+... 	font-size: 60px;
+... }
+... ''') #doctest: +NORMALIZE_WHITESPACE
+.cleanBox h1,
+.mod {
+	margin: 10px;
+}
+.cleanBox h1,
+.mod h1 {
+	font-size: 40px;
+}
+.cleanBox h1 {
+	font-size: 60px;
+}
+
+
+"""
+"""
+ADVANCED STUFF, NOT SUPPORTED (FROM SASS):
+--------------------------------------------------------------------------------
+http://sass-lang.com/docs/yardoc/file.SASS_REFERENCE.html
+
+Any rule that uses a:hover will also work for .hoverlink, even if they have other selectors as well
+>>> print css.compile('''
+... .comment a.user:hover { font-weight: bold }
+... .hoverlink { @extend a:hover }
+... ''') #doctest: +NORMALIZE_WHITESPACE
+.comment a.user:hover,
+.comment .hoverlink.user {
+	font-weight: bold;
+}
+
+
+Sometimes a selector sequence extends another selector that appears in another
+sequence. In this case, the two sequences need to be merged.
+While it would technically be possible to generate all selectors that could
+possibly match either sequence, this would make the stylesheet far too large.
+The simple example above, for instance, would require ten selectors. Instead,
+Sass generates only selectors that are likely to be useful.
+>>> print css.compile('''
+... #admin .tabbar a { font-weight: bold }
+... #demo .overview .fakelink { @extend a }
 ... ''') #doctest: +NORMALIZE_WHITESPACE
 #admin .tabbar a,
 #admin .tabbar #demo .overview .fakelink,