What does this function do?
_()
Can you link me to the relevant documentation, as searching for \"_\" is nigh on impossible?
Note sure I understand your question but here are some explanations for common scenarios.
If you open http://www.php.net/_ you get to the documentation of the _() function and see its for localization stuff (gettext).
_()
is an alias of gettext().
It's an alias for the gettext() function.