Layering with ENV based folder unclear

[fl-max]

The docs indicate the ability to layer tfvars using env based folders here and here. The first section (full-layering) seems to indicate this is "simple layering" but mentions the TS_ENV var without much explanation. The second section (extra) indicates the use of TS_ENV to organize based on env folders but doesn't explain.

Through trial and error I've learned that I need set both TS_ENV and TS_EXTRA like so: TS_ENV=$TS_ENV; TS_EXTRA=$TS_ENV/base. I think the Docs could use some added context here. Ideally, this should be supported out-of-the-box IMHO.