I meant to also add that the issue of what to do with links that don't resolve
once a document is assembled is a general one. The stylesheets could be customized to
simply ignore unresolved links, on the assumption that the link failure is due to
excluded content rather than a typo in the link. I don't know if there is a way for a stylesheet to distinguish between the two cases. It would be good for the
processor to at least emit an error message during processing so that such unresolved
links could be confirmed.

The other half of the problem making sure the written context of such a
disappearing link still makes sense. Putting links in the middle of a sentence risks
creating a garbled sentence if the link text disappears. I've written customizations where
the practice was to place such "soft" links as the sole content in a standalone
para, and if the link does not resolve, the entire para disappears. The link style in
that case included generating the surrounding text ("See ... for more information"). You
could also create an itemizedlist with role="relatedlinks" to contain them. Then the stylesheet could also omit the listitem container of an unresolved link, and the entire list and list title if none of the links resolve in the list.