So there is a proposal floating around for a fullsize attribute in HTML5... I am not in favor of it, because the effect the author of that proposal is trying to achieve MUST be controlled from A to Z by the web designer. So not only the animations, but also the closing button, the legend and its position, everything. I certainly don't want HTML and CSS to dive into that level of details. But wait, I said HTML and CSS? Hey, guys, look at the following. It took me exactly ten seconds to write it....

CSS chunk:

#full {
  display: none;
  position: relative;
}

#full:target {
  display: inline;
}

#full > img {
  position: absolute;
  z-index: 10000;
}

HTML chunk:

<a href="#full">
  <a id="full" href="#thumbnail">
    <img src="foo_full.jpg"/>
  </a>
  <img id="thumbnail" src="foo.jpg"/>
</a>

I know, I know, an anchor is not supposed to contain another anchor. Now, please, forget one second you're a web standards freak and look at my solution above. It just works...

Update: ROFL !!! I left a post on the fullsize attr's google group with a link to my post and the owner of the group has deleted my post ! Wow. That guy is apparently open to discussion, standardization and consensus....