# Variables from Doors and Windows In doors and windows the first combined element primarily determines the properties and the construction. Therefore its variables are passed on to the subsequent combined elements. These variables are now also forwarded to the HRB assignment when they have been defined there as external variables. In the opening settings or in the intermediate values in HRB the variables are used in the formulas. During the assignment the HRB interpreter takes the values for that specific opening at each opening. This enables very precise control of each individual window. This is suitable, for example, for transferring information about belt drives or the type of lower connection for floor-to-ceiling windows (balcony, terrace, façade). Special possibilities arise here when using IFC Premium: via the mappings the variables of the first combined element can be addressed directly. A specific value, for example "air at bottom", can thus be controlled via IFC, so that the requirement from the production planning can be transferred all the way into the HRB assignment. --- # 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://docs.dietrichs.com/dietrichs-intelligent-documentation/docs-de-en/holzrahmenbau-kompendium/prinzipien-des-hrb-systems/variablen/variablen-aus-turen-und-fenstern.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.