List of styles created on the fly

My xsl template changes source xml document from
<book><chapter><para> to <p class="book_chapter">,
<book><chapter><section><para> to <p class="book_chapter_section"> and so
on. Now I am looking for method, how to place list of all these new styles
(uniquely) at the beginning of output file. Note my output isn't .html
document, I use this format for explaining only.
I think for this purpose I cannot use mode attribute, because derived class
(style) is generated on the fly, it isn't present at beginning of
transformation, so I can't work with it like with standard nodes
(grouping/sorting) - it is text only.
My only idea is two pass process.
1) xml>xml_x - class converting
2) xml_x>my_output - all remaining transformations (building of list etc.)
Is there any way to do it by single pass? Thank you in advance for your tips
or link to any tutorial.