NB: This crate is part of the Rust compiler. For an overview of the
compiler as a whole, see
[the README.md file found in `librustc`](../librustc/README.md).
The `syntax` crate contains those things concerned purely with syntax
– that is, the AST ("abstract syntax tree"), parser, pretty-printer,
lexer, macro expander, and utilities for traversing ASTs.