Several system attributes use the 'Action' data type. Note: this data-type is not used or available for user-defined attributes.
Action-type attributes further divide into two discrete groups, as the action code they contain is used slightly differently by Tinderbox:
Although both an action and an expression are parts of Action code, the scope of what they (may) do differs. How they differ is explained in Expressions vs. Actions in Action code.
See also—notes linking to here: