how to change extents of a grob?

[Werner LEMBERG]

Dear LilyPonders,


I can get the extents of a grob with `ly:grob-extent`.  What is the
corresponding Scheme function to set the extents?

Or to ask in a different way: At the time when properties are
processed and you have to manipulate stencils, changing the stencil of
a grob doesn't change the extents of this grob, AFAICS.  How can I
adjust the extents at this stage to fit the dimensions of the stencil
(even if LilyPond no longer needs and/or uses the values for
positioning)?


    Werner