◄Directive Summary►  ◄Summary►
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  Syntax:  .ERRB <argument>
           .ERRNB <argument>
 
  .ERRB generates a severe error if argument is blank. .ERRNB generates
  an error if argument is not blank. Normally, these directives are used
  within macro definitions; a macro parameter is replaced by an empty
  string if you call the macro and do not give a corresponding argument.
  These directives let you write macros that generate an error if the
  wrong number of arguments are used in the macro call.
 
  argument   A name, number, or expression, though normally the name of
             a macro parameter.
 
  See Also:  .ERR, .ERR1, .ERRDEF, .ERRDIF, .ERRE, .ERRNZ
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