You can generate searchable docs from a .gir
(the thing that is built from scanning libvips and which in turn turn the typelib is made from) with g-ir-doc-tool, for example:
$ g-ir-doc-tool --language=Python -o ~/mydocs Vips-8.0.gir
Then to view them, either:
$ yelp ~/mydocs
Or perhaps:
$ cd ~/mydocs $ yelp-build html .
To make HTML docs. This is an easy way to see what you can call in the library.