Your right. The idea is really to fitter *remote* URIs, since remote resources are only allowed for audio and video in EPUB 3. I named the function `pf:is-absolute` but this is badly named.

Then I also faced a use case where a CSS include a file with sth like `url(//w3c.org/logo.png)` so I started testing for both schemed and absolute URIs in the `pf:is-absolute` function. So I decided to keep the name ;)

That said:

- I agree the name and implementation of the URI functions is not right, it should be fixed.
- in terms of functionality of the `html-to-fileset`, we should only check the remoteness. The other considerations about the file being under the same directory hierarchy should be handled beforehand, e.g along with the pre-processing done in `html-clean-resources.xsl` of the `html-to-epub3` script.