As you type the start of an AppleScript term, Script Debugger can fill in the rest of the term for you. This is essentially the Complete feature that appears in many other Cocoa applications, such as TextEdit. To see a list of possible completions:

• Type the beginning of an AppleScript term, then press Esc or choose Edit > Complete. A list of possible completions appears. (This list is drawn from scripting additions, AppleScript itself, and the tell context, along with relevant identifiers in the script itself.) Or, if there is just one known completion, the completion is simply entered for you and selected.

For example:

At this point you press Esc and browser window is filled in for you, because it is the only known completion. Continuing:

At this point you press Esc and a list of possible completions appears:

When the list appears you can navigate it with arrow keys. The Return key (and many other possible keys) will accept a selected completion, or you can double-click an entry in the list. The Esc or Delete key closes the list without inserting a completion.