Omitting :group [was: master 7936c8a: * lisp/mb-depth.el (minibuffer-depth-indicator): New face.]

[Drew Adams]

> This change causes a byte-compilation warning:
>   In toplevel form:
>   mb-depth.el:38:1: Warning: defface for
>   `minibuffer-depth-indicator' fails to specify
>   containing group

IMHO, we should adopt and promote a guideline
that it's a good, not a bad, idea to always
include an explicit `:group'.

I think that Stefan is quite opposed to this,
and he even goes to the trouble of removing
"unnecessary" `:group's.  Why?

AFAIK, the only advantage to omitting `:group'
is a little less verbose code.

The advantages to _not_ omitting `:group' are:

1. Local clarity - no need to look elsewhere.

2. Ability to move the thing elsewhere - its
   behavior/meaning wrt :group won't depend on
   its location.

To me, those advantages to not omitting `:group'
far outweigh the disadvantage.  But please point
out any advantage of omitting `:group' that I
may have missed.

It's good that `:group' is optional.  But it's
also good to get in the habit of not omitting
it, IMO, and that's a good practice to encourage.