[geocar]

Why not just:

    <a href="#fn-gcc" class="has-footnote">GCC[1]</a>
    …
    <p id="fn-gcc" class="marginnote"><label>1. </label>The GNU Compiler Collection</p>

It's compatible with the W3C recommended idiom for footnotes[2], is accessible without JavaScript, and you can still use `.marginnote` to provide CSS styling.

[2]: https://www.w3.org/TR/html5/common-idioms.html#footnotes

[gkya]

Well if this works it seems better, I'm mostly a user of hypertext so a bit ignorant, sorry.