Problem with mfrac example in 3.3.2.3

Hi,

The first example in 3.3.2.3 seems to have a problem (same as in MathML 2 
version). Shouldn't the <mfrac linethickness="2"> come right at the 
beginning, not after the first fraction? The graphic in 3.3.2.2 has both 
of the a,b fractions in the overall numerator, with c/d in the 
denominator. Shouldn't it be something like below (where &it; is used to 
give a rendering application a hint not to squash the two a,b fractions 
together horizontally, but nothing is here to suggest the smaller size for 
the c/d denominator, which may not be intended anyway):

      <mfrac linethickness="2">
<mrow>
  <mrow>
   <mo> ( </mo>
   <mfrac linethickness="0"> 
      <mi> a </mi>
      <mi> b </mi>
   </mfrac>
   <mo> ) </mo>
  </mrow>
  <mo>&it;</mo>
  <mrow>
   <mfrac>
      <mi> a </mi>
      <mi> b </mi>
   </mfrac>
  </mrow>
 </mrow> 
 <mfrac>
    <mi> c </mi>
    <mi> d </mi>
 </mfrac>
</mfrac>

Thanks.

John.