It seems that some links aren't converted correctly in the ?full=1 version of the Gentoo Handbook. More precisely the link to "Configuration File Protection" in hb-install-system.xml (?part=2&chap=4#doc_chap1) is converted to "#book_part2_chap4#doc_chap4". Bug noticed by Jocelyn Read <jsread@uwm.edu>
I'll look into that.
If only I could commit the solution
Cross-chapters links pointing inside a chapter (e.g. ?part=2&chap=4#doc_chap1) were simply not handled. The chapter number was extracted as '4#doc_chap1' i.e. what comes after 'chap='. There were two case in the handbook. guide.xsl and handbook.xsl fixed and committed.