Update tostring docs, plus more doc cleanup

docs/api/xmlstream/tostring.rst

@@ -1,17 +1,46 @@
-========
-tostring
-========
-
 .. module:: sleekxmpp.xmlstream.tostring
 
 .. _tostring:
 
 XML Serialization
------------------
+=================
+
+Since the XML layer of SleekXMPP is based on :mod:`~xml.etree.ElementTree`,
+why not just use the built-in :func:`~xml.etree.ElementTree.tostring`
+method? The answer is that using that method produces ugly results when
+using namespaces. The :func:`tostring()` method used here intelligently
+hides namespaces when able and does not introduce excessive namespace
+prefixes::
+
+    >>> from sleekxmpp.xmlstream.tostring import tostring
+    >>> from xml.etree import cElementTree as ET
+    >>> xml = ET.fromstring('<foo xmlns="bar"><baz /></foo>')
+    >>> ET.tostring(xml)
+    '<ns0:foo xmlns:ns0="bar"><ns0:baz /></foo>'
+    >>> tostring(xml)
+    '<foo xmlns="bar"><baz /></foo>'
+
+As a side effect of this namespace hiding, using :func:`tostring()` may
+produce unexpected results depending on how the :func:`tostring()` method
+is invoked. For example, when sending XML on the wire, the main XMPP
+stanzas with their namespace of ``jabber:client`` will not include the
+namespace because that is already declared by the stream header. But, if
+you create a :class:`~sleekxmpp.stanza.message.Message` instance and dump
+it to the terminal, the ``jabber:client`` namespace will appear.
 
 .. autofunction:: tostring
 
 Escaping Special Characters
 ---------------------------
 
+In order to prevent errors when sending arbitrary text as the textual
+content of an XML element, certain characters must be escaped. These
+are: ``&``, ``<``, ``>``, ``"``, and ``'``. The default escaping
+mechanism is to replace those characters with their equivalent escape
+entities: ``&amp;``, ``&lt;``, ``&gt;``, ``&apos;``, and ``&quot;``.
+
+In the future, the use of CDATA sections may be allowed to reduce the
+size of escaped text or for when other XMPP processing agents do not
+undertand these entities.
+
 .. autofunction:: xml_escape