Adobe After Effects CS4 - Manual (Page 687)

681 USING AFTER EFFECTS CS4
Expressions
Last updated 12/21/2009
Animating a brush stroke with an expression
Key attributes and methods (expression reference)
When you access a Key object, you can get time , index , and value properties from it. For example, the following
expression gives you the value of the third Position keyframe: position.key(3).value .
The following expression, when written on an Opacity property with keyframes, ignores the keyframe values and uses
only the placement of the keyframes in time to determine where a flash should occur:
d = Math.abs(time - nearestKey(time).time);
easeOut(d, 0, .1, 100, 0)
value Return type: Number or Array.
Returns the value of the keyframe.
time Return type: Number.
Returns the time of the keyframe.
index Return type: Number.
Returns the index of the keyframe.
MarkerKey attributes (expression reference)
You can access values for composition markers and layer markers using the same methods. Access layer markers
through the
thisLayer.marker object; access composition markers through the thisComp.marker object.
For the purpose of expressions, markers are a special type of Key object, so you can use methods such as
nearestKey(time) to access markers, and markers also have time and index attributes. The index attribute is not
the number (name) of the marker; it is the keyframe index number, representing the order of the marker in the time
ruler.
Expressions have access to all of the values for a marker that you can set in the Composition Marker or Layer Marker
dialog box. This expression on the Source Text property of a text layer displays the time, duration, index, comment
(name), chapter, URL, frame target, and cue point name for the layer marker nearest the current time, and whether
the marker is for an event cue point: