Description:
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Wouldn't it be nice if the trigger_error function could be called with a user-defined $errline and $errfile? Imagine you were writing an Abstract Class and wanted to handle class errors internally. Theoretically, you could retrieve the name of the current error handler by using the set_error_handler function and then the restore_error_handler function. Then, you could use call_user_func to trigger a user-defined error. However, if no error handler has been defined previously, set_error_handler will return null and the procedure would fail alltogether. On the other hand, calling trigger_error will show the file and line where the trigger_error function was called (which is very unuseful).

Test script:
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// Get the current error handler
function void ( $errno, $errstr ) { }
$error_handler = set_error_handler ( "void" );
restore_error_handler();

// User-define error
$error_arguments = array ( $errno, $errstr, $errfile, $errline );

// Trigger error
call_user_func ( $error_handler, $error_arguments ); // This will only work as long as an error handler has been previously set.

// Instead, the following function is proposed:
trigger_error ( string $error_msg, int $error_type = E_USER_NOTICE, string $error_file, string $error_line );