> This is so that users of gtk-doc don’t need to specify where docbook-xsl
> is to be searched for, right?

On the user-side, I don't know, but without this thee doc of WebKitGTK would
fail to build, so this is necessary on the builder side.

> Since generated HTML documentation tends to take a lot of space, what
> about moving it to a “doc” output?

Documentation is <7MB, <5% of the total package size, so I didn't bother
creating a separate output.
What do you think?

-- 
Pierre Neidhardt
https://ambrevar.xyz/