Added configuration-file syntax reference (#361)

* Added configuration-file syntax reference

doc/reference.rst

@@ -338,6 +338,147 @@ use-dependency-links, default: true
 versions, default 'versions'
   The name of a section that contains :ref:`version pins <pinned-versions>`.
 
+Configuration file syntax
+=========================
+
+Buildout configurations use an `INI file format
+<https://en.wikipedia.org/wiki/INI_file>`_.
+
+A configuration is a collection of named sections containing named
+options.
+
+Section names
+-------------
+
+A section begins with a section and and, optionally, a condition in
+square braces (``[`` and ``]``).
+
+A name can consist of any characters other than whitespace, square
+braces, curly braced (``{`` or ``}``), pound signs (``#``), colons
+(``:``) or semi-colons (``;``).  The name may be surrounded by leading
+and trailing whitespace, which is ignored.
+
+An optional condition is separated from the name by a colon and is a
+Python expression.  It may not contain a pound sign or semi-colon.  See
+the section on :ref:`conditional sections <conditional-sections>` for
+an example and more details.
+
+A comment, preceded by a pound sign or semicolon may follow the
+section name, as in:
+
+.. code-block:: ini
+
+   [buildout] # This is the buildout section
+
+.. -> header
+
+Options
+-------
+
+Options are specified with an option name followed by an equal sign
+and a value:
+
+.. code-block:: ini
+
+   parts = py
+
+.. -> option
+
+    >>> import six
+    >>> import zc.buildout.configparser
+    >>> def parse(s):
+    ...     return zc.buildout.configparser.parse(six.StringIO(s), 'test')
+    >>> from pprint import pprint
+    >>> pprint(parse(header + option))
+    {'buildout': {'parts': 'py'}}
+
+Option names may have any characters other than whitespace, square
+braces, curly braces equal signs or colons.  There may be and usually
+is whitespace between the name and the equal sign and the name and
+equal sign must be on the same line.
+
+Option values may contain any characters. A consequence of this is
+that there can't be comments in option values.
+
+Option values may be continued on multiple lines, and may contain blank lines:
+
+.. code-block:: ini
+
+   parts = py
+
+           test
+
+.. -> option
+
+Whitespace in option values
+___________________________
+
+Trailing whitespace is stripped from each line in an option value.
+Leading and trailing blank lines are stripped from option values.
+
+Handling of leading whitespace and blank lines internal to values
+depend on whether there is data on the first line (containing the
+option name).
+
+data on the first line
+  Leading whitespace is stripped and blank lines are omitted.
+
+  The resulting option value in the example above is:
+
+  .. code-block:: ini
+
+        py
+        test
+
+  .. -> val
+
+      >>> eq(parse(header + option)['buildout']['parts'] + '\n', val)
+
+no data on the first line
+  Internal blank lines are retained and common leading white space is stripped.
+
+  For example, the value of the option:
+
+  .. code-block:: ini
+
+     code =
+         if x == 1:
+             y = 2 # a comment
+
+             return
+
+  .. -> option
+
+  is::
+
+     if x == 1:
+         y = 2 # a comment
+
+         return
+
+  .. -> val
+
+       >>> eq(parse(header + option)['buildout']['code'] + '\n', val)
+
+Comments and blank lines
+------------------------
+
+Lines beginning with pound signs or semi-colons (``#`` or ``;``) are
+comments::
+
+  # This is a comment
+  ; This too
+
+.. -> comment
+
+       >>> eq(parse(comment + header + comment + option + comment )
+       ...    ['buildout']['code'] + '\n', val)
+
+As mentioned earlier, comments can also appear after section names.
+
+Blank lines are ignored unless they're within option values that only
+have data on continuation lines.
+
 .. [#root-logger] Generally, the root logger format is used for all
    messages unless it is overridden by a lower-level logger.
 

doc/topics/variables-extending-and-substitutions.rst

@@ -131,6 +131,8 @@ extends-cache buildout option <extends-cache-buildout-option>`.
 When a relative path is used in an extends option, it's interpreted
 relative to the path of the extending configuration.
 
+.. _conditional-sections:
+
 Conditional configuration sections
 ==================================
 

src/zc/buildout/tests.py

@@ -3785,6 +3785,7 @@ def clear_here():
             manuel.testing.TestSuite(
                 manuel.doctest.Manuel() + manuel.capture.Manuel(),
                 os.path.join(docdir, 'getting-started.rst'),
+                os.path.join(docdir, 'reference.rst'),
                 os.path.join(docdir, 'topics', 'bootstrapping.rst'),
                 os.path.join(
                     docdir,