state:modified.vars is a new selector, opt-in method behind the `st…

…ate_modified_compare_vars behavior` flag (off by default)

website/docs/reference/node-selection/methods.md

@@ -211,6 +211,7 @@ Because state comparison is complex, and everyone's project is different, dbt su
 - `state:modified.persisted_descriptions`: Changes to relation- or column-level `description`, _if and only if_ `persist_docs` is enabled at each level
 - `state:modified.macros`: Changes to upstream macros (whether called directly or indirectly by another macro)
 - `state:modified.contract`: Changes to a model's [contract](/reference/resource-configs/contract), which currently include the `name` and `data_type` of `columns`. Removing or changing the type of an existing column is considered a breaking change, and will raise an error.
+- `state:modified.vars`: Changes to [`vars`](/docs/build/project-variables) that a node depends on (available in v1.9 or with [dbt Cloud Versionless](/docs/dbt-versions/upgrade-dbt-version-in-cloud#versionless) via the `state_modified_compare_vars` [behavior flag](reference/global-configs/behavior-changes))
 
 Remember that `state:modified` includes _all_ of the criteria above, as well as some extra resource-specific criteria, such as modifying a source's `freshness` or `quoting` rules or an exposure's `maturity` property. (View the source code for the full set of checks used when comparing [sources](https://github.com/dbt-labs/dbt-core/blob/9e796671dd55d4781284d36c035d1db19641cd80/core/dbt/contracts/graph/parsed.py#L660-L681), [exposures](https://github.com/dbt-labs/dbt-core/blob/9e796671dd55d4781284d36c035d1db19641cd80/core/dbt/contracts/graph/parsed.py#L768-L783), and [executable nodes](https://github.com/dbt-labs/dbt-core/blob/9e796671dd55d4781284d36c035d1db19641cd80/core/dbt/contracts/graph/parsed.py#L319-L330).)