It's tough to know what you're really after, because it's not in everyday After Effects terminology: it has its own arcane terminology, y'know.
But I
THINK you may want to look at using Track Mattes to do what you seek. A text layer can be a track matte. Here's some info:
http://help.adobe.com/en_US/AfterEffects/9.0/WS3878526689cb91655866c1103906...
Don't worry if the help doesn't match your AE version; this stuff hasn't changed in decades.
Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA