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IFNB             Assemble If Argument Is Not Blank                  Directive

  IFNB <argument>
  statements
  [ELSE
  statements]
  ENDIF

    Initiates a conditional block, causing assembly of statements up to
    the optional ELSE directive, provided argument is not blank.

       Notes:     IFB and IFNB are usually used for conditional assembly
                  of macros based on the presence or absence of parameters
                  in the macro call.

                  Note that the angle brackets, <>, are required around
                  the argument.  The argument can be any name, number, or
                  expression.