You aren't going to be able to do this, I'm afraid. There is no exposed parameter in Motion that stores a text length. If you move the anchor to the right, then the text will be align right and the anchor won't move as the text length changes. What you CAN do, however, is rig a control to allow someone in Motion OR FCP X to manually adjust your mask to the text length by dragging a slider - or moving an on-screen control.
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Mark Spencer
Freelance Producer/Editor/Motion Graphics Artist
Apple-certified Master Trainer
Author, Motion 4 from Peachpit Press
http://www.applemotion.net
