Add some notes about Chameleon in the documentation

Author: xiaq

doc/customizing.txt

@@ -1642,11 +1642,42 @@ How the templates work
 ----------------------
 
 
+Templating engines
+~~~~~~~~~~~~~~~~~~
+
+Since version 1.4.20 Roundup supports two templating engines: the original
+`Template Attribute Language`_ (TAL) engine from Zope and the standalone
+Chameleon templating engine. Chameleon is intended as a replacement for the
+original TAL engine, and supports a syntax that is very similiar to the it,
+but they are not 100% compatible. The major (and most likely the only)
+incompatibility to worry about is the default expression type being
+``python:`` instead of ``path:``. See also "Incompatibilities and
+differences" section of `Chameleon documentation`__.
+
+**NOTE1**: For historical reasons, examples given below assumes path
+expression as default expression type. With Chameleon you have to manually
+resolve the path expressions. A Chameleon-based, z3c.pt, that is fully
+compatible with the old TAL implementation, is planned to be included in a
+future release.
+
+**NOTE2**: As of 1.4.20 Chameleon support is highly experimental and **not**
+recommended for production use.
+
+.. _Chameleon:
+   http://chameleon.repoze.org/
+.. _z3c.pt:
+   http://pypi.python.org/pypi/z3c.pt
+__ http://chameleon.repoze.org/docs/latest/reference.html#incompatibilities-and-differences
+.. _TAL:
+.. _Template Attribute Language:
+   http://dev.zope.org/Wikis/DevSite/Projects/ZPT/TAL%20Specification%201.4
+
+
 Basic Templating Actions
 ~~~~~~~~~~~~~~~~~~~~~~~~
 
 Roundup's templates consist of special attributes on the HTML tags.
-These attributes form the `Template Attribute Language`_, or TAL.
+These attributes form the **Template Attribute Language**, or TAL.
 The basic TAL commands are:
 
 **tal:define="variable expression; variable expression; ..."**
@@ -1743,10 +1774,6 @@ making arbitrary blocks of HTML conditional or repeatable (very handy
 for repeating multiple table rows, which would othewise require an
 illegal tag placement to effect the repeat).
 
-.. _TAL:
-.. _Template Attribute Language:
-   http://dev.zope.org/Wikis/DevSite/Projects/ZPT/TAL%20Specification%201.4
-
 
 Templating Expressions
 ~~~~~~~~~~~~~~~~~~~~~~