RE: What make the modeline update the major mode entry?

[Drew Adams]

> > Can someone please tell me what makes Emacs update the major mode
> > entry in the modeline?
> 
> grep for `mode-line-buffer-identification' in the Lisp source 
> code. You'll see plenty of hits like `dired-mode' and `info.el'
> - places where the variable is set.

Those locations set the format, but they do not update the display.

Depending on what you meant, you might also want to look for `mode_line_format'
and `display_mode_line' in `xdisp.c'. That seems to be where the actual
displaying takes place.