Why can't I mask dynamic text or device fonts yell's the inspiring flash developer!
It makes no sense! I can mask static text, why not dynamic text or device fonts?
Well Macromedia has a somewhat of an explanation here, but I'm going to try and explain this the best I can.
Basically you can only mask device fonts by using an actual movie clip as a mask.
You must also embed your dynamic text into a movie as well. You might not be used to this method as it's so convenient to use the timeline mask and most of the work you probably did in the past never required masking dynamic data loaded into a text field or text area. It's becoming so easy to generate external data in flash.