How does panopticlick detect fonts available in a browser?

You can determine if specific a font is installed or not by checking if text in that font has a different size than normal text (source).

But panopticlick.eff.org seems to be getting my complete list, are they just checking every they know of? I can't see that info in the HTTP Reque开发者_StackOverflow中文版st, is there just something in the DOM I can query for a list of available fonts?

Panopticlick uses Flash to retrieve the list of fonts installed on the client's computer.

In ActionScript:

var installedFonts = TextField.getFontList();
getURL('javascript:flashFontList("' + escape(installedFonts) + '")', '_self');