Copying attributes

Hi

Missing something obvious here.

I have this in the customisation layer:

<xsl:attribute-set name="revhistory.title.properties" use-attribute- 
sets="component.title.properties">
   <xsl:attribute name="font-weight">bold</xsl:attribute>
</xsl:attribute-set>

The 'bold' bit works, but it's not getting the styling from  
'component.titles.properties'.

Why is this?

And (assuming this is incorrect) how should you achieve this (that is,  
copying a style across and keeping DRY)?

Also, can anyone point me in the direction of the best place to find  
out how the various font styles inherit through docbook? I've found  
some documentation, but nothing comprehensive?

Thanks

Damon