| The `rustc_ast` crate contains those things concerned purely with syntax |
| – that is, the AST ("abstract syntax tree"), along with some definitions for tokens and token streams, data structures/traits for mutating ASTs, and shared definitions for other AST-related parts of the compiler (like the lexer and macro-expansion). |
| |
| For more information about how these things work in rustc, see the |
| rustc dev guide: |
| |
| - [Parsing](https://rustc-dev-guide.rust-lang.org/the-parser.html) |
| - [Macro Expansion](https://rustc-dev-guide.rust-lang.org/macro-expansion.html) |
