The BENEFIT. format differentiates between the employees who were hired on or before 31DEC79 and those who were hired after that date. Employees hired on or before 31DEC79 are eligible for a benefits package, those hired after are not. The first range in BENEFIT. uses the LOW keyword and the SAS date constant '31DEC79'D to include all variable values up to and including December 31, 1979. For values that fall into this range, the format uses the WORDDATEw. format. WORDDATEw. is a format supplied by SAS.(footnote 1) 
      value benefit  low-'31DEC79'd=[worddate20.]
FOOTNOTE 1:  For more information on SAS date constants, see the section on dates, times, and intervals in SAS Language Reference: Concepts. For complete documentation on WORDDATEw., see the section on formats in SAS Language Reference: Dictionary. [arrow]