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IF               Initiate Conditional Block                    MASM Directive

  IF expression
  statements
  [ELSE
  statements]
  ENDIF

    Initiates a conditional block, causing the assembly of statements up
    to the optional ELSE directive, provided that expression is true
    (evaluates to a nonzero value).

       Notes:     IF directives may be nested to 255 levels.

                  The statements following IF and ELSE can be other IF
                  conditional blocks.

                  If the condition if false (evaluates to a zero value)
                  and an ELSE directive is included, the statements
                  between the ELSE and ENDIF will be assembled.

                  A nested ELSE directive is matched with the nearest IF
                  directive that does not have an ELSE directive.

                  The expression for the IFE directive must resolve to an
                  absolute value and must not be a forward reference.