In olden days, when the -me macro set was written, troff offered only three environments (.ev request), numbered 0, 1, and 2.  In its implementation, the -me macro set uses these historical environments internally for things such as page headers and footers and footnotes.  This meant that in historical troff, environments were unavailable to end users of -me.

Groff changed this situation by expanding the number of environments from three to infinity.  The -me documentation was never updated to reflect this new situation.

This might be OK.  A number of things that troff itself associates with an environment (such as type size and line spacing), -me stores in registers, which are always global across environments.  Many -me macros (such as the various paragraph macros: .pp, .lp, .ip, etc.) set these attributes based on the respective registers every time they're invoked.  So properties that are per-environment in troff tend to be global under normal -me usage.  (See http://lists.gnu.org/archive/html/groff/2012-03/msg00005.html for more about this.)

Conversely, it might make sense to go ahead and document the expanded environment functionality now available to -me users, even though it won't act precisely as in generic troff.

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If it is decided that the documentation should be so updated, new text would need to explain the use of environments in -me, and how to avoid colliding with -me's internal use of environments.  Additionally:

• "environments" would need to be added to the -Me Reference Manual's opening paragraph telling what general troff knowledge the manual presumes
• the .ev and .evc requests should be added to the manual's index, which includes, in addition to all the macros -me defines, "selected troff requests... [that] can generally be used with impunity."

(This issue was tangentially mentioned in comment 6 of bug #55060.)