Inside Macintosh: AppleScript Language Guide / Part 2 - AppleScript Language Reference

Chapter 3 - Values / Using Value Class Definitions

Commands Handled

Commands are requests for action. Simple values cannot respond to commands, but composite values can. For example, lists can respond to the Count command, as shown in the following example.

count {"This", "list", "has", 5, "items"}
--result: 5

Each composite value class definition includes a "Commands Handled" section that lists commands to which values of that class can respond.