#10713: Improve documentation for \b and \B and add a few tests. Initial patch and tests by Martin Pool.
diff --git a/Doc/library/re.rst b/Doc/library/re.rst
index df3f9e5..74e33b9 100644
--- a/Doc/library/re.rst
+++ b/Doc/library/re.rst
@@ -325,14 +325,19 @@
Matches the empty string, but only at the beginning or end of a word. A word is
defined as a sequence of alphanumeric or underscore characters, so the end of a
word is indicated by whitespace or a non-alphanumeric, non-underscore character.
- Note that ``\b`` is defined as the boundary between ``\w`` and ``\W``, so the
- precise set of characters deemed to be alphanumeric depends on the values of the
- ``UNICODE`` and ``LOCALE`` flags. Inside a character range, ``\b`` represents
- the backspace character, for compatibility with Python's string literals.
+ Note that formally, ``\b`` is defined as the boundary between a ``\w`` and
+ a ``\W`` character (or vice versa), or between ``\w`` and the beginning/end
+ of the string, so the precise set of characters deemed to be alphanumeric
+ depends on the values of the ``UNICODE`` and ``LOCALE`` flags.
+ For example, ``r'\bfoo\b'`` matches ``'foo'``, ``'foo.'``, ``'(foo)'``,
+ ``'bar foo baz'`` but not ``'foobar'`` or ``'foo3'``.
+ Inside a character range, ``\b`` represents the backspace character, for compatibility with Python's string literals.
``\B``
Matches the empty string, but only when it is *not* at the beginning or end of a
- word. This is just the opposite of ``\b``, so is also subject to the settings
+ word. This means that ``r'py\B'`` matches ``'python'``, ``'py3'``, ``'py2'``,
+ but not ``'py'``, ``'py.'``, or ``'py!'``.
+ ``\B`` is just the opposite of ``\b``, so is also subject to the settings
of ``LOCALE`` and ``UNICODE``.
``\d``