◄Directive Summary►  ◄Summary►  ◄IF Block Syntax►
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  Syntax:  IFB <argument>
           IFNB <argument>
 
  IFB causes assembly of a block of statements (see IF Block Syntax)
  if argument is blank. IFNB causes assembly of a block of statements
  if argument is not blank.
 
  Within a macro, a parameter name is replaced by an empty string if you
  call the macro without giving a corresponding argument. IFB and IFNB
  therefore let you define default behavior when an argument is missing.
 
  The ELSEIFB and ELSEIFNB correspond to IFB and IFNB, respectively.
 
  argument   Any name, number, or expression; typically, the name of
             a parameter of a macro.
 
  See Also: IF, IFE, IF1, IFDEF, IFDIF
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