[OE-core] curious about proper use of "REALPV" re: versioning pre-release recipes

[Robert P. J. Day]

  digging through YP dev tasks manual, section 3.3.18, "Properly
Versioning Pre-Release Recipes", and the admittedly minimal usage of
that feature in oe-core doesn't really seem to bolster the
description.

  in YP manual, example for irssi recipe:

  REALPV = "0.8.16-rc1"
  PV = "0.8.15+${REALPV}"

first, there's nothing magic about the variable "REALPV", is there? it
could just as easily be, say, RDAY, or one could simply forego the use
of a variable entirely and write:

  PV = "0.8.15+0.8.16-rc1"

correct?

  second, the only example of that feature in all of oe-core is
cdrtools-native_3.01.bb, which contains:

  PV = "3.01a31+really3.01"
  REALPV = "3.01"

but that doesn't seem to match what is in the YP manual, as the recipe
filename version contains just "3.01", so this doesn't seem like a
situation where that feature is necessary. indeed, it seems like
cdrtools-3.01 has been out since 2015:

  https://sourceforge.net/projects/cdrtools/files/

so it's unclear why this recipe doesn't just use 3.01.

  finally, there are two recipes under meta-oe that *do* incorporate
the "-rc" qualifier in their recipe filename:

  recipes-graphics/ftgl/ftgl_2.1.3-rc5.bb
  recipes-connectivity/libnet/libnet_1.2-rc3.bb

but, oddly, neither uses the feature described above. i'm just
pointing out that what one reads in that YP manual doesn't match its
actual usage in the current code base.

rday