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docs: clarify that a reserved rule must exist in the grammar

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Amaan Qureshi 2025-08-28 00:49:34 -04:00 • committed by Amaan Qureshi
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docs/src/creating-parsers/2-the-grammar-dsl.md
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@ -133,12 +133,13 @@ than globally. Can only be used with parse precedence, not lexical precedence.
[*node types* file][static-node-types].
- **`reserved`** — similar in structure to the main `rules` property, an object of reserved word sets associated with an
array of reserved rules. The reserved rule in the array must be a terminal token meaning it must be a string, regex, or token,
or a terminal rule. The *first* reserved word set in the object is the global word set, meaning it applies to every rule
in every parse state. However, certain keywords are contextual, depending on the rule. For example, in JavaScript, keywords
are typically not allowed as ordinary variables, however, they *can* be used as a property name. In this situation, the `reserved`
function would be used, and the word set to pass in would be the name of the word set that is declared in the `reserved`
object that corresponds to an empty array, signifying *no* keywords are reserved.
array of reserved rules. The reserved rule in the array must be a terminal token meaning it must be a string, regex, token,
or terminal rule. The reserved rule must also exist and be used in the grammar, specifying arbitrary tokens will not work.
The *first* reserved word set in the object is the global word set, meaning it applies to every rule in every parse state.
However, certain keywords are contextual, depending on the rule. For example, in JavaScript, keywords are typically not allowed
as ordinary variables, however, they *can* be used as a property name. In this situation, the `reserved` function would be used,
and the word set to pass in would be the name of the word set that is declared in the `reserved` object that corresponds to an
empty array, signifying *no* keywords are reserved.
[bison-dprec]: https://www.gnu.org/software/bison/manual/html_node/Generalized-LR-Parsing.html
[ebnf]: https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form