In going through the MPEP I ran into this jewel in 2111.03 Transitional Phrases:
For the purposes of searching for and applying prior art under 35 U.S.C. 102 and 103, absent a clear indication in the specification or claims of what the basic and novel characteristics actually are, “consisting essentially of” will be construed as equivalent to “comprising.”
Being equivalent to comprising helps a lot. I used to worry quite a bit over these transitional phrases when used in software patents. Although this doesn’t add clarity for “consisting of” without “essentially”, it is still very helpful. Why anyone would have used “consisting” for software is beyond me, but patents with such claims are out there.