Update textfile.Substfile documentation

1 files changed, 9 insertions, 11 deletions

diff --git a/src/engine/SCons/Tool/textfile.xml b/src/engine/SCons/Tool/textfile.xml
index c5e586bc..428a318c 100644
--- a/src/engine/SCons/Tool/textfile.xml
+++ b/src/engine/SCons/Tool/textfile.xml
@@ -110,11 +110,10 @@ blob.txt
 <builder name="Substfile">
 <summary>
 <para>
-The &b-Substfile; builder generates a single text file
-by concatenating the source files.
-Nested lists of sources are flattened. 
-&cv-LINESEPARATOR; is used to separate the source files;
-see the description of &b-Textfile; for details.
+The &b-Substfile; builder creates text file from another file or set of
+files by concatenating them with &cv-LINESEPARATOR; and replacing text
+using &cv-SUBST_DICT; construction variable. Nested lists of source files
+are flattened. See also &b-Textfile;.
 </para>
 
 <para>
@@ -132,20 +131,19 @@ are automatically added to the target if they are not already present.
 <para>
 If a construction variable named &cv-SUBST_DICT; is present,
 it may be either a Python dictionary or a sequence of (key,value) tuples.
-If the former,
-the dictionary is converted into a list of tuples in an arbitrary order,
+If it is dictionary,
+it is converted into a list of tuples in an arbitrary order,
 so if one key is a prefix of another key
 or if one substitution could be further expanded by another subsitition,
 it is unpredictible whether the expansion will occur.
 </para>
 
 <para>
-Any occurences in the source of a key
+Any occurences of a key in the source
 are replaced by the corresponding value,
 which may be a Python callable function or a string.
-If a value is a function,
-it is first called (with no arguments) to produce a string.
-The string is <emphasis>subst</emphasis>-expanded
+A function is called with no arguments to get a string.
+Strings are <emphasis>subst</emphasis>-expanded
 and the result replaces the key.
 </para>