From any script you can issue a call to a handler which belongs to the script of an object. You encapsulate such calls in a tell theObject statement, where theObject refers to the owner of the script.

In a tell statement you refer to the object itself with the special variable it:

tell window 1 to AddOne(it)

The verbs ("AppleEvents") which are given in the dictionary and which support a direct parameter follow a special rule concerning their target: Smile automatically redirects them to the direct parameter. Thus the two following lines are equivalent:

close window 1 saving ask

tell window 1 to close it saving ask