.z in SAS

Question

I found this paper in SAS, which includes (on the first page and some other parts) the following line of code:

if trt1pn > .z then...

I was wondering what the purpose of this is. I have never seen the expression ".z" before. I though (and some of my colleagues thought the same way), it was a typo. But you can do

data kk;
   a = .z;
   b = .b;
run;

and you get a variable equal to "Z", and a variable b - "B".

Where is this discussed in SAS manuals? What does it mean? Why is it used in paper in this way?

Answer 1

SAS 28 (.,._,.A-.Z) '.' . , . , ".N".

, ( proc).

Proc format;
  Value Response
    1='Yes'
    0='No'
    .U='Unsure'
    .N='Not Applicable'
    .R='Refused to Answer';
Run;

Answer 2

28 (._, ., .A, .B,..., .Z). "", . - (._) -Z (.Z). , :

if trt1pn > .Z then ...

missing():

if not missing(trp1pn) then ...

.