AppleScript: The Definitive Guide, 2nd Edition

Element Specifiers

Referring to a property is easy; you just use the name of the property. For example:

get version of application "Finder" -- 10.4.2

Referring to an element is harder. An object can have any number of each class of element, so you must say which one(s) you mean. To do this, you use an element specifier (or just specifier for short—AppleScript also calls this a key form). A specifier has two components: the name of a class and some way of picking out the right one(s). AppleScript has eight built-in forms of specifier, and these are the only ones you are allowed to use. The next eight sections describe those eight specifier forms.

(Actually, there are actually nine element specifiers. I don't discuss middle because it is rarely used. Plus, a reference to a property is actually a form of specifier, so I guess that makes ten. The variety of specifier forms makes a specifier quite an interesting and complicated part of an Apple event. The repeated pattern involving the four terms form, want, seld, and from in Example 3-1 denotes a specifier.)

In real life, it will rarely be open to you to use just whichever specifier form you please on a particular occasion. Given a certain application, object, and class of element, only certain specifier forms will work, and experimentation is the best guide as to which ones they are. An application's dictionary is supposed to help you here, but it might not, or might not be accurate (see "Defective Element Specifiers" in Chapter 20). ...