For quite some time, we've been outputting HTML pages with a half-doctype declaration, with no DTD specified:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
Browsers interpret such a doctype as not quite reliable, and render pages in so-called "quirks" mode for backwards compatibility with the parsing and rendering bugs of earlier versions. It's been occasionally suggested that it's superior to include also a URL to the DTD, which will put browsers into a stricter, standards-compliant mode:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
A couple days ago I slipped this in. All well and good in Mozilla, but in Internet Explorer 6.0 (I haven't tried 5.x) this triggers a selection bug, such that trying to select text with the mouse selects everything from the beginning of the document to the point where you've got the mouse, instead of the portion of text you're dragging over. Not very helpful.
Since, unfortunately, a lot of people use this dreadful program, and this is a _really_ annoying browser bug, I've temporarily taken the DTD reference back out, so we're back to quirks mode, where selection works.
Sigh...
-- brion vibber (brion @ pobox.com)