handler is a string containing the name of a function that must exist when xml_parse() is called for parser.
The function named by handler must accept two parameters:
parser, is a reference to the XML parser calling the handler.
Character data handler is called for every piece of a text in the XML document. It can be called multiple times inside each fragment (e.g. for non-ASCII strings).
If a handler function is set to an empty string, or
FALSE, the handler
in question is disabled.
Instead of a function name, an array containing an object reference and a method name can also be supplied.