counting nodes

Hallo,

thanks a lot for answering my last question. 
Now, i have to count different nodes and i can't find a solution.
Perhaps someone can point me to.
I want to count all descenders and all ascenders.
In this example the solution is 2 descenders and 2 ascenders:
 
<output>
    <features>
          <feature name="descender-g" />
          <feature name="descender-y" />
          <feature name="ascender-h" />
          <feature name="ascender-l" />
    </features>
</output>

Thats my try:

<xsl:for-each select="//feature">
<xsl:value-of select="substring-before(@name,'-')='descender'"/>
</xsl:for-each>

The function substring() is working. But count(substring(...)) not.
I have to count the true results. How can i solve this problem? 

Thanks, Katrin.