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url: /snippets/how-to/macros-option.md
---
Rewrites AST nodes before they are printed, without forking the generator. Each [macro](/docs/5.x/guide/going-further/macros) callback (such as `schema` or `operation`) receives the node and a context object, and returns a replacement or `undefined` to leave it as is. Omitted callbacks keep their defaults, and macros run in order, so a later one sees the output of an earlier one.