Pascal with extensions for object-oriented multiprogramming by Jim Welsh and D. Bustard of Queens University, Belfast, UK. Pascal Plus uses an "envelope" construct for both packages and classes.

["Pascal Plus - Another Language for Modular Multiprogramming", J. Welsh et al, Soft Prac & Exp 9:947 (1979)].

["Sequential Program Structures", J. Welsh et al, P-H 1984, ISBN 0-13806828-3].