Visit http://en.wikipedia.org/w/api.php?action=parse&page=USB&prop=sections
Some of the entries have crazy html in them, such as (see the part that says "line":
{ "toclevel": 3, "level": "4", "line": "<span></span><span></span><span></span><span></span><span></span>Prereleases", "number": "2.1.1", "index": "4", "fromtitle": "USB", "byteoffset": 13726, "anchor": "Prereleases" },
This is due to the markup for that section being
==== {{anchor|0.7|0.8|0.9|0.99|1.0RC}}Prereleases ====
which translates to
==== <span id="0.7"></span><span id="0.8"></span><span id="0.9"></span><span id="0.99"></span><span id="1.0RC"></span>Prereleases ====
and when the parser strips attributes but leaves the <span> tags it gives the result shown. Tidy (probably) fixes it on WMF sites, but why generate it in the first place?