We are used to using the automatic variables _n_ to identify the iteration count, or the boolean _error_ variable to identify data / logic errors when performing DATA step processing.
The same variables are not available to us in PROC steps.
While the code:
data part ; set sashelp.class ; where _n_ > 4 ; run ;
will work, the code:
proc print data = sashelp.class ; where _n_ > 4 ; run ;
will not.