Sets the character data handler function for the XML parser
handler is a
string containing the name of a function that must exist when
xml_parse() is called for
The function named by
handler must accept
handler ( resource parser, string data )
The first parameter, parser, is a reference to the XML parser calling the handler.
The second parameter,
the character data as a string.
If a handler function is set to an empty string, or FALSE, the handler in question is disabled.
TRUE is returned if the handler is set up, FALSE if
parser is not a parser.
Note: Instead of a function name, an array containing an object reference and a method name can also be supplied.