Number of elements with a given attribute

Hello,

In a piece of theater, I have some verses that are split between different
roles.

All verses without a part attribute are complete verses.
<role name='...'>
  <verse>...</verse>
  <verse>...</verse>
  ...
</role>

The other are tagged on the following model:
<role name='...'>
   ...
  <verse>...</verse>
  <verse part="beginning">...</verse>
</role>
<role name='...'>
  <verse part="continuation">...</verse>
</role>
<role name='...'>
  <verse part="continuation">...</verse>
</role>
<role name='...'>
  <verse part="end">...</verse>
  <verse>...</verse>
  ...
</role>

I need to know if a continuation is the only one between beginning and end,
the first or the second of two, the first, second or third of three, and so
on.

<xsl:value-of select="count(preceding::verse[@part != 'beginning']) "/> gives
me the count of all preceding verses with part attribute other
than "beginning" from the beginning of the piece, what is not what I want.
I wish to have the count of preceding parts of verse from the last beginning
part.

Could someone help me?

Thanks in advance,
Ph. Faehndrich