If set to a valid callback, this will be used to generate the error
context for an error. For PHP-related errors, this will be a file and line number as retrieved from debug_backtrace(), but can be customized for other purposes. The error might actually be in a separate configuration file, or in a database query.
Set an error Callback If set to a valid callback, this will be called every time an error is pushed onto the stack. The return value will be used to determine whether to allow an error to be pushed or logged.
The return value must be one of the ERRORSTACK_* constants.
This functionality can be used to emulate PEAR's pushErrorHandling, and the PEAR_ERROR_CALLBACK mode, without affecting the integrity of the error stack or logging
Error message parameters passed into push() will be used as input for the error message. If the template is 'message %foo% was %bar%', and the parameters are array('foo' => 'one', 'bar' => 'six'), the error message returned will be 'message one was six'