like SVG icon files. They are injected so that they can be colored via CSS.

Example CSS

body { content: fetch-url('./icon.svg'); }

Output when run on an empty HTML file:

<html>
  <body><!-- DEBUG: Transcluded file './icon.svg' -->
    <svg xmlns="http://www.w3.org/2000/svg" version="1.1">
      <rect x="25" y="25" width="200" height="200" fill="lime" stroke-width="4" stroke="pink" />
    </svg>
  </body>
</html>

Refs https://github.com/Connexions/cnx-easybake/pull/41

Some things to note:

having a comment or something might be helpful in debugging where this file came from
there is cruft <?xml .... that needs to be stripped out
We might need to validate that we transcluded XML
sourcemaps should probably mark the entire SVG file when it it transcluded

openstax / css-manipulate

fetch files and inject them #11

Example CSS