how does shr-use-fonts choose fonts?

[Eric Abrahamsen <eric@ericabrahamsen.net>]

When I set shr-use-fonts to t, Chinese characters in incoming emails are
displayed in a mixture of fonts. Elsewhere in Emacs, all Chinese
characters are displayed using:

xft:-arphic-AR PL New Sung-normal-normal-normal-*-15-*-*-*-*-0-iso10646-1 (#x2B2D)

I don't know how Emacs settled on that font, but it looks fine.

Inside Gnus messages with shr-use-fonts set to t, some characters are
displayed with the above font, others with:

arexft:-Misc-Fixed-normal-normal-normal-ja-13-*-*-*-c-120-iso10646-1 (#xCF2)

Apparently a Japanese font. I don't know how one is chosen over the
other. In this line:

我明天给你回信

The first three characters are in the Japanese font, the next two in
Chinese, and the last two back in Japanese again. It looks awful!

With shr-use-fonts set to nil, the Chinese font is used for all
characters, including Gnus messages.

I'm running git Emacs, on Linux, with no desktop environment. My
~/.Xdefaults file has:

Emacs.font: Inconsolata-13

But that's the only Emacs-specific line in there. Elsewhere in my init
I've got:

(require 'chinese)
(require 'china-util)

But I just commented those out and restarted, and the same thing
happens. I can't think of any more relevant config stuff...

Any help appreciated!

Eric