unknown function in opensips/opensips.cfg

[ghost]

In line 378 and 379,I found a function $ctime().But I can't find the function in opensips official documents.Could you please explain the function?Thanks very much

[ghost]

And the code is as below:

	$var(tz) = $ctime(min);
	$var(tm) = ($ctime(min) % 10);