[CAS] Inconsistency with commands.

[CH3791]

Sorry for yet another post guys but,

I am getting confused about the difference between uppercase and lowercase commands. For some cases there doesn't seem to be a difference.
STRING(); works the same as string();
LOCAL; works the same as local; **I think...**

But in other commands, they act a bit weird. I have found 2 so far:

Code:

#cas
char_program(input):=
BEGIN
  return char(input);
END;
#end

Inputing 8730 returns an empty box. Apparently, I've used the wrong case for "CHAR". This is despite how in CAS mode, when you select the "CHAR" command from Toolbox > Catlg > "CHAR", it is given to you in lowercase. In this case, only CHAR works.

Code:

#cas
expr_program(input):=
BEGIN
  return EXPR(input);
END;
#end

Inputing "a" returns "Error: Syntax Error". Instead of EXPR, expr is needed here. Although selecting "EXPR" from the CAS toolbox does give it in lowercase, it is displayed in uppercase in the catalog.

What is the difference between the cases, and how should I know which one to use?