[CSS21] WD 8.3: editorial: incomplete reference

<margin-width>, including the 'auto' value, may be used for margin-top
and margin-bottom as well as for margin-left and margin-right, whereas
currently the reference for the behaviour of 'auto' refers only to
section 10.3 (widths), not 10.6 (heights).

Please change the end of the reference to:

  | ... for behaviour in 'margin-right' and 'margin-left', or the section
  | on <a href="visudet.html#Computing_heights_and_margins" >calculating
  | heights and margins</a> for behaviour in 'margin-top' and
  | 'margin-bottom'."

(If someone can suggest a wording that covers use in the 'margin'
shorthand property then that would be better.  Maybe don't mention
property names, just refer to both sections: "See the sections on ... and
... for behaviour.", or "See sections 10.3 and 10.6 for behaviour.".)

pjrm.