Or, what ever other tag is meaningful
for your project.
I have tagged all releng maps (and related
builder files) with R3_1_2, except for Dali maps, which I tagged with R2_2_2.
While the map files are the "final
authority" on what was included with a release, having a common tag
often helps when you are working with many modules at once, such as comparing
how HEAD is different from 3.1.2 release.