"re-throw" from custom error handler? error patterns?

I was wondering is it possible to "re-throw" an error that one has caught with a custom error handler if, for example, I only wanted to deal with the errors generated by the library I was working on? Or perhaps some way to only catch a custom defined error type? I suppose I'm trying to overload the trigger_error method to work like exceptions and perhap that isn't the appropiate thing to do. Is there a consensed upon pattern for dealing with error conditions in PHP? I'm finding that using trigger_error was very natural for me as the author of a tool/library (Magpie an RSS parser) but it makes it very difficult for my users to cope with the errors. Thanks, Kellan