Adobe After Effects - Manual (Page 681)

[10, 23]
You can assign an Array object to a variable, making it easy to refer to array values in other areas of the expression. For example:
myArray = [10, 23]
The dimension of an Array object is the number of elements in the array. The dimension of myArray is 2. Different properties in After Effects have
different dimensions depending on the number of value arguments they have. In the expression language, the values of properties are either
single values (Number objects) or arrays (Array objects).
The following table provides examples of some properties and their dimensions:
You can access the individual elements of an Array object by using brackets and an index number to indicate which element you want. The
elements in an Array object are indexed starting from 0. Using the previous example, myArray[0] is 10 and myArray[1] is 23.
The following two expressions are equivalent:
[myArray[0], 5]
[10, 5]
The Position property arrays are indexed as follows:
position[0] is the x coordinate of position.
position[1] is the y coordinate of position.
position[2] is the z coordinate of position.
Colors are represented as four-dimensional arrays [red, green, blue, alpha]. In projects with a color depth of 8 bpc or 16 bpc, each value in a color
array ranges from 0 (black) to 1 (white). For example, red can range from 0 (no color) to 1 (red). So, [0,0,0,0] is black and transparent, and
[1,1,1,1] is white and completely opaque. In projects with a color depth of 32 bpc, values under 0 and over 1 are allowed.
If you use an index that is greater than the index of the highest-dimension component in an Array object, After Effects returns an error. For
example, myArray[2] causes an error, but position[2] returns the z coordinate of Position.
Many of the properties and methods in the After Effects expression language take Array objects as arguments or return them as values. For
example, thisLayer.position is an Array object that is either two-dimensional or three-dimensional depending on whether the layer is 2D or
3D.
If you want to write an expression that keeps the y value of an animation of Position but fixes the x value at 9, you would use the following:
Dimension Property
1 Rotation °
Opacity %
2 Scale [x=width, y=height]
Position [x, y]
Anchor Point [x, y]
Audio Levels [left, right]
3 Scale [width, height, depth]
3D Position [x, y, z]
3D Anchor Point [x, y, z]
Orientation [x, y, z]
4 Color [red, green, blue, alpha]
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