Problems with signs law and other arithmetic operators

[compsystems]

5+ SPC +6 => 11 OK
5- SPC -6 => 11 OK

Where is the information to use the +, -, ++, -- operator?, some of my classmates who bought the hpprime are disappointed that no information as hpprime works, without documentation we have to guess.
Please HPPrime TEAM complete catalog help

NOW with − as sign /!\ ASC("−") = 8722 the command should be called Unicode() and non-ASCII ASC()

−−6 => 6 ok
−+6 => -6 ok
5-−6 => 11 ok

5▶x
x++ => 6 ok
x-- => 5 ok

--x => ERROR
++x => ERROR

And not say what type of error, it is necessary to clearly define the errors displayed on screen, not only display an icon of (X) with the input typed in the input line.

All power calculator is lost in these bit details