A single compile-time builtin, ''SUBSTR'', was added.
Also in '''1966''' Robert Rosin published a pair of articles<ref>{{cite journal|last=Rosin|first=Robert|title=PL/I Macro Processor - Progress Report|journal=PL/I Bulletin|yeardate=August 1966|month=August|issue=2|url=http://www.iron-spring.com/PLI_Bulletins/PLI_Bulletin_2.pdf|accessdate=January 22, 2013}}</ref><ref>{{cite journal|last=Rosin|first=Robert|title=Macros in PL/I|journal=PL/I Bulletin|yeardate=August 1966|month=August|issue=2|url=http://www.iron-spring.com/PLI_Bulletins/PLI_Bulletin_2.pdf|accessdate=January 22, 2013}}</ref> discussing development of the preprocessor. This development was based in a "[[SHARE (computing)|SHARE]] XXVI Memo" from earlier the same year and a paper by Mark Elson. Rosin credits [[MAD (programming language)|MAD]] as the only previous example of a macro processor in a high-level language.
