bug#37213: Execute set-window-margins. left-margin-width remains 0.

[martin rudalics <rudalics@gmx.at>]

 > The documentation says "This variable specifies the width of the left
 > margin".  As best, this is unclear.  What you're saying is that the
 > variable ceases to specify that width, should the margin be altered by
 > other means.

Eli didn't say that.

 > I maintain that this is either a bug in the documentation, or in the
 > code.
 >
 > If the former, it should explicitly state that the variable is
 > write-only, and its read value is undefined.  It should say that the
 > function window-margins should be used instead.

The variable is not write-only and its read value is well-defined.

 > But it might be easier just to amend the code.  There appear to be just
 > two ways to set the width of the left margin (or the right margin), so
 > if it gets set the second way, why not just set that variable?  Could
 > this do any harm?  (Note: I haven't looked at the code, yet.)

Please re-read the documentations of 'left-margin-width' and
'set-window-margins' having in mind that the same buffer may appear in
different windows and the same window may show different buffers all
with differing margins.

Once you've done that, please look at the respective documentations
for fringes and scroll bars which are even more complicated because
they have to obey a frame parameter as well.

Thanks, martin