but anywhere there's a tricky word that might need further explanation.

Not really. A footnote's purpose is to put additional information at the bottom of the page. It was invented for a printed page world, and doesn't need to exist in a hypertext world, where information should be always right where it's needed.

For example, look at the use of the <acronym> tag at http://www.csszengarden.com/?cssfile=/204/204.css

I appreciate what you're trying to do, but I could imagine it would confuse users who expect to see a floating "Three Letter Acronym" but instead get a floating box stating

Any suggestions for removing the top and bottom lines of this box (i.e. remove the references to footnotes)?

You can also add this code to your CSS stylesheet

 .footnotes-footer{ display:none; } 

my 2. try: ( Helmuti_pdorf) using collapsible block:

 [[collapsible show="+ show me the hidden abbr/explanations (a.k.a. footnotes)" hide="- abbr/explanations"]] (attributes: show - text to be shown when folded, e.g. "+ show text" hide - text to be shown when unfolded, click to fold hideLocation - location of the text to hide block, values are: top, bottom, both (nice for long blocks) ) [[footnoteblock title=""]] [[/collapsible]] 

Test of whether invisible footnotes would suffice for something like HTML¹ <abbr> or <acronym> tag functionality.
Test of another text with TLA².
Test of another text with ETLA³.
Test of another text with SFLA⁴.
Test of another text with LFLA⁵.
Test of another text with VLFLA⁶.

blabla1

bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla TLA⁷ bla bla bla bla bla bla bla bla
bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla
bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla bla .

1. try from "andrewescott" was:
[[div style="color: white"]]
[[footnoteblock title=""]]
[[/div]]

in action:

but anywhere there's a tricky word that might need further explanation.

Is this not exact the functionality of a footnote?

Also, the whole thing is much more complex than the simple functionality I'm trying for. It's something that is widely supported in browsers, and is used not just for acronyms and abbreviations, but anywhere there's a tricky word that might need further explanation.

The other approach would be to define some a:hover rules in the CSS and tie them to links in the page, but this is a very messy approach and is not what that was designed for.

All I am after is basic HTML functionality! :)

And only use the "arising text by hoovering over the text" ?

http://www.wikidot.com/doc:wiki-syntax#toc29

I think he means the "hoovering" text- and how this is possible in wikidot.

( on images this is with the alt=",,," attribute, but on text I cannot image)