If I run xprop on my emacs I see this:
WM_CLASS(STRING) = "emacs", "Emacs23"
You might want to read X11 documentation. WM_CLASS is always a two-element list; the first string is appName aka resource name, and the second is className. This has been true since X11R4 introduced WM_CLASS.
xmonad has used them this way since at least 0.2.