> For the complete documentation index, see [llms.txt](https://dynamopythonprimer.gitbook.io/dynamo-python-primer/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://dynamopythonprimer.gitbook.io/dynamo-python-primer/4-revit-specific-topics/built-in-categories.md). # 4.12 Built-In Categories #### Built-In Categories The Revit user-interface shows many categories to users, such as Doors, Floors and Generic Models. However, Revit internally keeps track of a much more detailed list of categories, called Built-in categories. The full list of Built-in categories can be found in the [BuiltInCategory Enumeration](https://apidocs.co/apps/revit/2019/ba1c5b30-242f-5fdc-8ea9-ec3b61e6e722.htm) - these are hard coded and we can't create more of them. #### Retrieving Elements of a BuiltInCategory Because the list covers nearly 1000 categories, it helps programmers target Revit elements with much greater precision. Built-in categories can be especially useful for FilteredElementCollectors, letting us retrieve highly-specific kinds of elements. For instance, to collect all area tags in a document: ```python #Boilerplate Code area_tags = FilteredElementCollector(doc).OfCategory(BuiltInCategory.OST_AreaTags).ToElements() OUT = area_tags ``` Combined with the usual [boilerplate code](/dynamo-python-primer/getting-started/boilerplate-setup-code.md), the above code will rapidly fetch all area tags in a document.\ It is this level of precision which makes BuiltInCategories especially useful when coding. --- # 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://dynamopythonprimer.gitbook.io/dynamo-python-primer/4-revit-specific-topics/built-in-categories.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.