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            plvasp
          ( | aspect ); | 
Selects the largest viewport with the given aspect ratio within the subpage that leaves a standard margin (left-hand margin of eight character heights, and a margin around the other three sides of five character heights).
aspect
          (PLFLTRatio of length of y axis to length of x axis of resulting viewport.
      Redacted form: plvasp(aspect)
    
This function is used in example 13.