-part of the crescendo hairpin, making it invisible. The rectangle is
-defined as postscript code within a text markup.
-
-To fine-tune the position and size of the markup, the number preceding
-@code{setgray} in the postscript definition can be set to a value less
-than one, making it grey. The two numbers before @code{scale} in the
-postscript code are responsible for the width and height of the
-rectangle, the two numbers before @code{translate} change the x- and
-y-origin of the rectangle.