Описание тега modula-2
Modula-2 is a procedural programming language, created as a revision of Pascal. It was intended to fix shortcomings of Pascal which its designer, Niklaus Wirth, intended only as an instructional language. Modula-2 supports separate definition and implementation modules, coroutines, data abstraction, machine access support, and an extensive standard library for I/O, math, etc.
The Stack Overflow use of this tag is for questions related to any dialect or superset implementation of Modula-2.
The language and library documentation is the book Programming in Modula-2, 3rd edition, Springer Verlag, Berlin, 1985, by Niklaus Wirth. ISBN 978-0387116747
The Wikipedia article links to over two dozen implementations, four dialects, eight supersets, and eight derivative languages.