Suppose you want to modify a package named "foo" in the distribution.
Because the package exist, you are tempted to change is name, to avoid conflict.
This is in PKGBUILD set pkgname=foome.
But then you realize pkgname is use in many place in the PKGBUILD, like "cd ${pkgname}".
So you say, I will add a new field called upname=foo. And I will replace all occurences (except the first) to ${upname}. Later you realize that you have to add provides=${upname} and conflicts=${upname} for it to replace correctly the foo package. At this state I think things become to work. But if I submit changes to this PKGBUILD I might be looked strangely. Thinks would be easier however if packages where already using this trick...
Maybe I should just bump the pkgrel field to a high value.