Mystery Prime commands

[Joe Horn]

When you type a nonexistent command word by itself in CAS, it just gets returned as-is, like "bananna" in the screenshot below. When you type an existing command by itself in CAS, it either gets returned with single-quotes around it, like 'factor' below, or it returns an error string, like "Mod" below, or it pops up a "Syntax Error" box, like "esac" below.



Since typing all of the following commands by themselves in CAS pops up a syntax error, I assume that they are either undocumented CAS commands, or undocumented Prime commands of some sort, possibly program structure commands. Anybody know what these mystery commands are, and what their syntax is? The first three are clearly normal commands spelled backwards. How many more undocumented commands are hidden in Prime?

esac
fi
elif
localbloc
proc
otherwise
try_catch
stack
default