# Id The controlId is an essential part of a brixxbox Control. Every Control needs a unique (in its App) Id. All new controls get a generated Id (starting with an underscore). The generated Id is changeable but once you give your control a custom Id, this will be unchangeable afterwards. The generated Id should never be used to reference the control. If you need to do something with the control (like hide it, get or set a value), you need to give it a readable Id. A Control is always addressed with its controlId. Control Ids should start with a lowercase (often with a mandatory prefix, that has been set in the app) and can contain, Numbers, upper and lowercase letters and underscores. --- # Agent Instructions: 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: ``` GET https://brixxbox.gitbook.io/brixxbox-documentation/configuration/app-editor/app-editor-properties/id.md?ask= ``` The question should be specific, self-contained, and written in natural language. 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.