Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide

Comparisons involving the DATE attribute and a non-literal

In comparisons where one comparand has the DATE attribute and the other is not a date and not a literal, the compiler issues an E-level message. The non-date value is treated as if it had the same date pattern as the other comparand and as if it had the same window.

  dcl start_date char(6) date;
  dcl non_date char (6);

  if start_date >= non_date then /* windowed */
  ...
Rational Developer for System z
PL/I for Windows, Version 8.0, Programming Guide