About Expressions			Expression Input Paths
Chapter 24, Expressions

In cases where you may not want to type the full name of a custom attribute when this attribute has been added at the same level as the attribute being expressed, you can enter expressions that refer to an input by its short name.

For example, if you want to add an expression to the Gaussian Rotation based on the value of the Gaussian X Radius, instead of writing out the long expression, you only need to refer to its short expression.