Add suport for attr_lists in table headers.

4 files changed, 20 insertions, 7 deletions

diff --git a/docs/change_log/release-3.3.md b/docs/change_log/release-3.3.md
index f826082..0e0bb89 100644
--- a/docs/change_log/release-3.3.md
+++ b/docs/change_log/release-3.3.md
@@ -43,6 +43,9 @@ be separated from the rest of the content by at least one space. This makes it e
 lists defined on inline elements within a cell and the attribute list for the cell itself. It is also more consistent
 with how attribute lists are defined on other types of elements.
 
+The extension has also added support for defining attribute lists on table header cells (`<th>` elements) in the same
+manner as data cells (`<td>` elements).
+
 In addition, the documentation for the extensions received an overhaul. The features (#987) and limitations (#965) of the extension are now fully documented.
 
 ## New features
diff --git a/docs/extensions/attr_list.md b/docs/extensions/attr_list.md
index d9f4d68..d3d5e12 100644
--- a/docs/extensions/attr_list.md
+++ b/docs/extensions/attr_list.md
@@ -156,6 +156,8 @@ Note that in the first column, the attribute list is preceded by a space; theref
 (`<td>` element). However, in the second column, the attribute list is not preceded by a space; therefore, it is
 assigned to the inline element (`<em>`) which immediately preceded it.
 
+Attribute lists may also be defined on table header cells (`<th>` elements) in the same manner.
+
 ### Limitations
 
 There are a few types of elements which attribute lists do not work with. As a reminder, Markdown is a subset of HTML
diff --git a/markdown/extensions/attr_list.py b/markdown/extensions/attr_list.py
index d02194e..9a67551 100644
--- a/markdown/extensions/attr_list.py
+++ b/markdown/extensions/attr_list.py
@@ -79,7 +79,7 @@ class AttrListTreeprocessor(Treeprocessor):
             if self.md.is_block_level(elem.tag):
                 # Block level: check for attrs on last line of text
                 RE = self.BLOCK_RE
-                if isheader(elem) or elem.tag in ['dt', 'td']:
+                if isheader(elem) or elem.tag in ['dt', 'td', 'th']:
                     # header, def-term, or table cell: check for attrs at end of element
                     RE = self.HEADER_RE
                 if len(elem) and elem.tag == 'li':
diff --git a/tests/test_syntax/extensions/test_attr_list.py b/tests/test_syntax/extensions/test_attr_list.py
index 3d65761..6baaafb 100644
--- a/tests/test_syntax/extensions/test_attr_list.py
+++ b/tests/test_syntax/extensions/test_attr_list.py
@@ -39,9 +39,10 @@ class TestAttrList(TestCase):
         self.assertMarkdownRenders(
             self.dedent(
                 """
-                | valid on td | inline      | empty | missing space | not at end   |
+                | A { .foo }  | *B*{ .foo } | C { } | D{ .foo }     | E { .foo } F |
                 |-------------|-------------|-------|---------------|--------------|
                 | a { .foo }  | *b*{ .foo } | c { } | d{ .foo }     | e { .foo } f |
+                | valid on td | inline      | empty | missing space | not at end   |
                 """
             ),
             self.dedent(
@@ -49,11 +50,11 @@ class TestAttrList(TestCase):
                 <table>
                 <thead>
                 <tr>
-                <th>valid on td</th>
-                <th>inline</th>
-                <th>empty</th>
-                <th>missing space</th>
-                <th>not at end</th>
+                <th class="foo">A</th>
+                <th><em class="foo">B</em></th>
+                <th>C { }</th>
+                <th>D{ .foo }</th>
+                <th>E { .foo } F</th>
                 </tr>
                 </thead>
                 <tbody>
@@ -64,6 +65,13 @@ class TestAttrList(TestCase):
                 <td>d{ .foo }</td>
                 <td>e { .foo } f</td>
                 </tr>
+                <tr>
+                <td>valid on td</td>
+                <td>inline</td>
+                <td>empty</td>
+                <td>missing space</td>
+                <td>not at end</td>
+                </tr>
                 </tbody>
                 </table>
                 """