> For the complete documentation index, see [llms.txt](https://docs.atfinity.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.atfinity.io/rule-language/operators/list-operators/in.md). # in ### Description `in` is used to check if a value is present in a list or a [taxonomy](/guides/glossary/taxonomy.md). If it is, the expression evaluates true. On the left side of `in`, there is always a single value. The list of options, which could be a taxonomy, goes on the right side of `in`. ### Example If a [document](/guides/glossary/document.md) is only relevant to parties who reside in the European Union, attach this condition to it: ``` p is Person p.domicile in EUCountries ``` There is one answer for what the domicile of a person or an entity is, so this is a single value. With the expression in the example, you check whether this value is part of the taxonomy `EUCountries`, which predictably consists of a list of all the member states of the European Union. If `p.domicile` is the United Kingdom, the condition evaluates to false. The document will not be included in the [case](/guides/glossary/case.md). If `p.domicile` is Belgium, the condition evaluates to true, meaning the document is included. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://docs.atfinity.io/rule-language/operators/list-operators/in.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.