How to find the font?

[Jan Willem Stumpel <jstumpel@planet.nl>]

This question is not Debian-specific.

I am working in X (not in "text mode"), and some text is displayed
in some application; e.g. in iceweasel, but it could be something
else. So a part of my screen is filled with some text, in some
font, or in various fonts.

Is there any way to find out which fonts are actually being used?
I mean, ideally I would like to be able to select a part of the
displayed text, and then some application, daemon, or whatever,
would say, e.g.: "this is Freemono, at 16 points". Is this possible?

Regards, Jan