access to :style-sheet from <lisp> tag

Hi,

If we have a style defined:

(muse-derive-style "my-xhtml" "xhtml"
		   :style-sheet "<link rel=\"stylesheet\" type=\"text/css\" media=\"all\"
                                href=\"include/style.css\" />")

and we want to write a header file for the projects using this derived
style, what variable can be used inside a <lisp> tag to insert the
contents of :style-sheet above?  For the projects using the xhtml style, I
can use <lisp>muse-xhtml-style-sheet</lisp>, but what's the variable for a
derived style?  Thanks.

Cheers,

--

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Seb