nsISAXContentHandler in Firefox 2.0

 Receive notification of character data.

 The Parser will call this method to report each chunk of
 character data.  SAX parsers may return all contiguous character
 data in a single chunk, or they may split it into several chunks;
 however, all of the characters in any single event must come from
 the same external entity so that the Locator provides useful
 information.

 Note that some parsers will report whitespace in element
 content using the ignorableWhitespace method rather than this one
 (validating parsers must do so).

 @param value the characters from the XML document

 Receive notification of the end of a document.

 There is an apparent contradiction between the documentation for
 this method and the documentation for ErrorHandler.fatalError().
 Until this ambiguity is resolved in a future major release,
 clients should make no assumptions about whether endDocument()
 will or will not be invoked when the parser has reported a
 fatalError() or thrown an exception.

 The SAX parser will invoke this method only once, and it will be
 the last method invoked during the parse.  The parser shall not
 invoke this method until it has either abandoned parsing (because
 of an unrecoverable error) or reached the end of input.

 Receive notification of the end of an element.

 The SAX parser will invoke this method at the end of every
 element in the XML document; there will be a corresponding
 startElement event for every endElement event (even when the
 element is empty).

 For information on the names, see startElement.

 @param uri the Namespace URI, or the empty string if the
        element has no Namespace URI or if Namespace
        processing is not being performed
 @param localName the local name (without prefix), or the
        empty string if Namespace processing is not being
        performed
 @param qName the qualified XML name (with prefix), or the
        empty string if qualified names are not available

 End the scope of a prefix-URI mapping.

 See startPrefixMapping for details.  These events will always
 occur immediately after the corresponding endElement event, but
 the order of endPrefixMapping events is not otherwise guaranteed.

 @param prefix The prefix that was being mapped. This is the empty
               string when a default mapping scope ends.

 Receive notification of ignorable whitespace in element content.

 Validating Parsers must use this method to report each chunk of
 whitespace in element content (see the W3C XML 1.0
 recommendation, section 2.10): non-validating parsers may also
 use this method if they are capable of parsing and using content
 models.

 SAX parsers may return all contiguous whitespace in a single
 chunk, or they may split it into several chunks; however, all of
 the characters in any single event must come from the same
 external entity, so that the Locator provides useful information.

 @param whitespace the characters from the XML document

 Receive notification of a processing instruction.

 The Parser will invoke this method once for each processing
 instruction found: note that processing instructions may occur
 before or after the main document element.

 A SAX parser must never report an XML declaration (XML 1.0,
 section 2.8) or a text declaration (XML 1.0, section 4.3.1) using
 this method.

 @param target the processing instruction target
 @param data the processing instruction data, or null if
        none was supplied.  The data does not include any
        whitespace separating it from the target

 Receive notification of the beginning of a document.

 The SAX parser will invoke this method only once, before any
 other event callbacks.

 Receive notification of the beginning of an element.

 The Parser will invoke this method at the beginning of every
 element in the XML document; there will be a corresponding
 endElement event for every startElement event (even when the
 element is empty). All of the element's content will be reported,
 in order, before the corresponding endElement event.

 This event allows up to three name components for each element:

 1.) the Namespace URI;
 2.) the local name; and
 3.) the qualified (prefixed) name.

 Any or all of these may be provided, depending on the values of
 the http://xml.org/sax/features/namespaces and the
 http://xml.org/sax/features/namespace-prefixes properties:

 The Namespace URI and local name are required when the namespaces
 property is true (the default), and are optional when the
 namespaces property is false (if one is specified, both must be);

 The qualified name is required when the namespace-prefixes
 property is true, and is optional when the namespace-prefixes
 property is false (the default).

 Note that the attribute list provided will contain only
 attributes with explicit values (specified or defaulted):
 #IMPLIED attributes will be omitted.  The attribute list will
 contain attributes used for Namespace declarations (xmlns*
 attributes) only if the
 http://xml.org/sax/features/namespace-prefixes property is true
 (it is false by default, and support for a true value is
 optional).

 @param uri the Namespace URI, or the empty string if the
        element has no Namespace URI or if Namespace
        processing is not being performed
 @param localName the local name (without prefix), or the
        empty string if Namespace processing is not being
        performed
 @param qName the qualified name (with prefix), or the
        empty string if qualified names are not available
 @param atts the attributes attached to the element.  If
        there are no attributes, it shall be an empty
        SAXAttributes object.  The value of this object after
        startElement returns is undefined

 Begin the scope of a prefix-URI Namespace mapping.

 The information from this event is not necessary for normal
 Namespace processing: the SAX XML reader will automatically
 replace prefixes for element and attribute names when the
 http://xml.org/sax/features/namespaces feature is
 true (the default).

 There are cases, however, when applications need to use prefixes
 in character data or in attribute values, where they cannot
 safely be expanded automatically; the start/endPrefixMapping
 event supplies the information to the application to expand
 prefixes in those contexts itself, if necessary.

 Note that start/endPrefixMapping events are not guaranteed to be
 properly nested relative to each other: all startPrefixMapping
 events will occur immediately before the corresponding
 startElement event, and all endPrefixMapping events will occur
 immediately after the corresponding endElement event, but their
 order is not otherwise guaranteed.

 There should never be start/endPrefixMapping events for the
 "xml" prefix, since it is predeclared and immutable.

 @param prefix The Namespace prefix being declared. An empty
               string is used for the default element namespace,
               which has no prefix.
 @param uri The Namespace URI the prefix is mapped to.