much from 2.x API, and sites that use
CodeMirror in a very simple way might be able to upgrade without
trouble. But it does introduce a number of incompatibilities. Please
at least skim this text before upgrading.</p>

<p>Note that <strong>version 3 drops full support for Internet
Explorer 7</strong>. The editor will mostly work on that browser, but
it'll be significantly glitchy.</p>

<section id=dom>
  <h2>DOM structure</h2>

<p>This one is the most likely to cause problems. The internal
structure of the 