The commonly recommended way to use text item delimiters is like this:
set tid to AppleScript\'s text item delimiters
set AppleScript\'s text item delimiters
I found this tidbit on https://developer.apple.com/library/mac/#documentation/applescript/conceptual/applescriptlangguide/conceptual/ASLR_fundamentals.html in the section AppleScript Fundamentals > Global Constants in AppleScript > text item delimiters:
If you change the text item delimiters property in Script Editor, it remains changed until you restore its previous value or until you quit Script Editor and launch it again. If you change text item delimiters in a script application, it remains changed in that application until you restore its previous value or until the script application quits; however, the delimiters are not changed in Script Editor or in other script applications you run.