Animating with the Channel Editor > Expressions > About Expressions >
Expression Content

An expression is composed of numeric values, constants, channel references, or combinations of these used with arithmetic operators. Expressions are calculated from left to right, according to a specific order defined in Operator Precedence.

For example, the following expression contains channel references and multiplies the transparency value of image1 by 2 to affect the transparency of image2 across all keyframes.

Channel | Expression
--- | ---
image2.material.transparency | image1.material.transparency* 2