The pllegend and plcolorbar routines are available in PLplot to
      provide users with the capability of visually annotating their plots
      with a legend (a series of patterned boxes, lines, or symbols with
      associated explanatory UTF-8 text) or a color bar (an annotated
      subplot representing a continuous range of colors within the main
      plot and typically identifying certain colors with certain numerical
      values using an axis). pllegend is useful for visually annotating
      most two-dimensional plots.  See our standard examples 04 and26 for some
      examples.  plcolorbar is especially useful for annotating continuous
      shade plots generated by plshades.  See our standard example 16, for an
      example.
    
      The pllegend and plcolorbar routines provide the users
      complete and convenient control of the size and position of the
      results on the plot and also return size data that makes it
      straightforward to stack different legend or colorbar results together
      on the plot (see our standard example
      33 for an example of this capability).  Furthermore, the
      pllegend and plcolorbar routines provide the user with many
      different style possibilities for the results.  Because of all these
      features, pllegend and plcolorbar have an extensive argument list.
      So we recommend first-time users of pllegend and plcolorbar use
      our standard examples 04, 16, and 26 as a tutorial
      on how to use these PLplot capabilities in a simple way, and for more
      advanced use we recommend studying the pllegend and plcolorbar
      documentation and also our standard example
      33 which attempts to exercise most capabilities of these two
      PLplot functions.