ISO/IEC TS 21544:2018 This document describes extensions to the C++ Programming Language (Clause 2) that introduce modules, a functionality for designating a set of translation units by symbolic name and ability to express symbolic dependency on modules, and to define interfaces of modules. These extensions include new syntactic forms and modifications to existing language semantics.
ISO/IEC 14882 provides important context and specification for this document. This document is written as a set of changes against that specification. Instructions to modify or add paragraphs are written as explicit instructions. Modifications made directly to existing text from ISO/IEC 14882 use underlining to represent added text and strikethrough to represent deleted text.