(part of the nitpickiness of some of these questions stems from
that, in my updated courseware, i want to use actual examples out of,
say, the openembedded layer, and not just contrived examples involving
packages like "foo" and "bar". to that end, i want to be able to
explain why some recipes are written the way they are and, conversely,
to explain why some recipes might look weird.)

the bitbake manual has a reasonable explanation of
DEFAULT_PREFERENCE but there are examples in the OE layer that seem to
not be written as cleanly as they could be.

consider under recipes-devtools the two directories "pkgconfig" and
"pkgconf", and the respective .bb files:

- pkgconfig_git.bb
- pkgconf_1.6.3.bb

the pkgconfig recipe file does *not* contain a PROVIDES setting, while
pkgconfig_1.6.3.bb does:

PROVIDES += "pkgconfig"

so, given that, one expects that other recipes should have a
DEPENDency on "pkgconfig", which could be satisfied by either of
those.

however, oddly, the file pkgconf_1.6.3.bb contains the line:

DEFAULT_PREFERENCE = "-1"

which seems odd as there don't appear to be any other recipes that
provide pkgconfig, and AIUI, the default provider for any recipe is
the recipe with *exactly* the same name as the target -- in this case,
"pkgconfig".

so while that DEFAULT_PREFERENCE line doesn't hurt anything, in this
specific case (assuming i haven't overlooked any other recipes that
provide pkgconfig), that DEFAULT_PREFERENCE line is superfluous,
correct?

rday