(PHP 4, PHP 5, PHP 7)
xml_set_processing_instruction_handler — Set up processing instruction (PI) handler
   Sets the processing instruction (PI) handler function for the XML parser
   parser.
  
A processing instruction has the following format:
<?
?>
    ?>) can not be quoted,
   so this character sequence should not appear in the PHP code you embed
   with PIs in XML documents.If it does, the rest of the PHP code, as well
   as the "real" PI end tag, will be treated as character data.
  
 
parserA reference to the XML parser to set up processing instruction (PI) handler function.
handler
       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
       three parameters:
       
$parser
        , string $target
        , string $data
        )parsertargettarget, contains the PI
           target.
          
         datadata, contains the PI
           data.
          
         
       If a handler function is set to an empty string, or FALSE, the handler
       in question is disabled.
      
Note: Instead of a function name, an array containing an object reference and a method name can also be supplied.
   Returns TRUE on success or FALSE on failure.