Description
string 
set_exception_handler ( callback exception_handler )
   Sets the default exception handler if an exception is not caught within a
   try/catch block. Execution will stop after the
   exception_handler is called.
  
   The exception_handler must be defined before calling
   set_exception_handler(). This handler function needs to accept
   one parameter, which will be the exception object that was thrown.
  
Return Values
   Returns the name of the previously defined exception handler, or NULL on error. If
   no previous handler was defined, NULL is also returned.