Unfortunately, there is no xsl:function support in XSL 1.0, so
we have to duplicate the existing code :/
For more details about the attribute scopes / types, see:
https://lists.osmocom.org/pipermail/openbsc/2020-October/013278.html
Change-Id: I7f7e6e32c156de24dcc80166a29119e6dda8c169
Related: SYS#4937
The manuals existed in different form for several years in an internal
sysmocom repository. However, since they had just recently been
converted from docboox-xml to asciidoc and all files have been
re-shuffled for enabling the public release, there's not much point in
keeping the history with git-filter-branch.