Apple Motion 4 - Manual (Page 1469)

The upper area of the Sequence Text controls contains the Add and Remove pop-up
menus, which are used to select parameters to add to the behavior, or to remove
parameters. The second group of parameters are the Sequence controls, which include
options for setting the direction of the animation, whether the animation is applied per
character, per word, or per text layer, and so on.
Sequence controls
Add or Remove
parameters
3 In the Parameter row, click the Add pop-up menu, choose Format, then choose Scale.
The Scale parameter is added to the behavior and is set to 100% by default (which
represents the original size of the text).
4 Set Scale to the largest (or smallest) value you want the text to become in your animation.
In this example, the Scale value is set to 350%. To enter separate values for the X and Y
scale, click the Scale disclosure triangle.
1469 Appendix E Obsolete Text Behaviors