What does "E2" and "E3" stand for in a program listing?

[4ster]

If there is a tutorial on little used functions in program listings, please point me to it.

I ran across a couple of instructions I don't understand in a program here:
Arabic to Roman

Lines
04 E3
31 E2

Also, when using rwiker's web site http://rwiker.github.io/hp41barcode/# to generate bar code, is there a symbol to use for the "Append" function on the 41? I've been manually re-entering lines because the symbol for "Append" is not documented on the site.

Sorry for the basic questions. I do feel a little outside my pay grade here.