[aur-general] About PKGBUILD of the automatic nightly builds

Recently,I was attracted by the songbird and nightingage media player based on Mozilla Tech.And I noticed these to nightly build PKGBUILD in AUR whose pkgver is part of a shell command string,and I want to do something to make that pkgver recognised by the AUR interface. Anyone who can tell me how to write a automatic nightly build PKGBUILD?Or,is there any standard on nightly build PKGBUILD? Thanks! bin32-songbird-nightly:https://aur.archlinux.org/packages.php?ID=44366 songbird-nightly-bin:https://aur.archlinux.org/packages.php?ID=32932