Sets the default 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.This may be the XML declaration,
document type declaration, entities or other data for which
no other handler exists.
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.