gh-54358: Clarify data chunking in pyexpat (GH-31629)

Co-authored-by: Éric Araujo <merwok@netwok.org>

Author: slateny

Doc/library/pyexpat.rst

@@ -214,7 +214,8 @@ XMLParser Objects
    :meth:`CharacterDataHandler` callback whenever possible.  This can improve
    performance substantially since Expat normally breaks character data into chunks
    at every line ending.  This attribute is false by default, and may be changed at
-   any time.
+   any time. Note that when it is false, data that does not contain newlines
+   may be chunked too.
 
 
 .. attribute:: xmlparser.buffer_used
@@ -372,7 +373,10 @@ otherwise stated.
    marked content, and ignorable whitespace.  Applications which must distinguish
    these cases can use the :attr:`StartCdataSectionHandler`,
    :attr:`EndCdataSectionHandler`, and :attr:`ElementDeclHandler` callbacks to
-   collect the required information.
+   collect the required information. Note that the character data may be
+   chunked even if it is short and so you may receive more than one call to
+   :meth:`CharacterDataHandler`. Set the :attr:`buffer_text` instance attribute
+   to ``True`` to avoid that.
 
 
 .. method:: xmlparser.UnparsedEntityDeclHandler(entityName, base, systemId, publicId, notationName)