Strange?

[address@hidden]

Dear listmembers,
I am currently trying to go through the documentation - it's something like 
1000 pages, so this takes time :-). I am using octave 5.2.0. When I say

>> A=5;
>> A
A =  5
>> isvarname (A)
ans  =  0

shouldn't this be "1" rather than "0"? The manual states "Return true if name 
is a valid variable name". In my example I consider "A" a valid variable name, 
isn't it? So, could you shed some light on what I am doing wrong here?
Thank you,
take care

Dieter