Can't define new page mode correctly in Conkeror

I can't seem to get even a basic new page mode working in 开发者_如何学运维Conkeror.

In my .conkerorrc I have this:

define_page_mode("bz_mode", "BZ");
auto_mode_list.push([/bugzilla/, bz_mode]);

The documentation suggests (at least to me) that this should be sufficient. But when I visit (say) bugzilla.mycompany.com, I don't see the new mode indicated in Conkeror's mode line.

What's the correct way to do this?

So it turns out the trick is to say

define_page_mode("bz_mode", $display_name = "BZ");

instead.