Text expression selectors and comments on After Effects Help:
"The text animation system in After Effects is complex. It's very, very powerful... but it's complex. Perhaps the most complex and difficult part of the whole system is how selectors work. And within that subset, the most esoteric and powerful feature is expression selectors. Few people use them, because they're hard to figure out; but those who do use them have a great tool in their hands. ... That's where Aaron Cobb came along."Aaron thanks Dan Ebberts, who helps out on Creative Cow (reference 1, 2).