gistfile1.txt

   Statement Modifiers
       Any simple statement may optionally be followed by a SINGLE modifier, just before the
       terminating semicolon (or block ending).  The possible modifiers are:

           if EXPR
           unless EXPR
           while EXPR
           until EXPR
           when EXPR
           for LIST
           foreach LIST

       The "EXPR" following the modifier is referred to as the "condition".  Its truth or
       falsehood determines how the modifier will behave.

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