How to determine whether executing within trigger

I vaguely seemed to recall seeing a standard Oracle package / function along these lines, but I can't seem to find it now... Is there a way to determine whether the current execution is operating inside a trigger? There are certain statements (primarily transaction control, DDL) that cannot be executed within a trigger (unless there in an autonomous transaction routine, at which point they're "outside" the trigger context).
TIA,
   Michael Received on Wed Nov 28 2007 - 11:56:11 CST