Inquiry regarding undocumented <Apron> priority encoding for "Force draw above runways/markings"

Hello MSFS SDK Team,

While working on advanced scenery design tools and analyzing compiled XML structures, we discovered an interesting and undocumented behavior regarding the element’s properties.

In the MSFS Scenery Editor, users can check the boxes for “Force draw above runways” and “Force draw above markings” on an Apron object. However, looking at the compiled XML output, no specific boolean attributes are added to the tag (which is expected, as the official XML schema does not define them).

Instead, we observed that the editor encodes these boolean flags directly into the priority attribute by adding a high offset in the 2-billion range. For example:

  • A standard priority of 5 with both flags active is exported as:
    <Apron … priority=“2000000005” …>

Writing this specific priority value directly into the XML successfully forces the coloration/apron to render above runways and markings without any manual adjustments in the Scenery Editor afterwards.

We would like to request clarification on the following points:

  1. Is this specific high-value encoding for the priority attribute a fully supported, stable, and future-proof behavior that third-party tools can safely rely on?
  2. Are there plans to introduce dedicated, human-readable XML attributes (e.g., drawAboveRunways=“TRUE” and drawAboveMarkings=“TRUE”) in future SDK updates to make the XML schema more explicit and standardized?

Thank you very much for your insight and for your continued efforts in improving the MSFS developer ecosystem!

Best regards,
Claus

Hello @MumbaiJi ,

Yes this is future-proof and you can use it safely.
And from what I’ve heard, it’s going to stay like that.

ok, but please get it documented in the SDK documentation.

But such “hidden” parameters, which are mixed in other unrelated parameters, may make it difficult to code in XML directly. So why not use explicite parameters for certain aspects?

Hello @MumbaiJi ,

The bug has been logged on our side.
Thanks for reporting the issue.

Hi Roman, thanks.

Is there a list available for undocumented features in the SDKs for MSFS 2020 and MSFS 2024?

Currently, there is no list cataloging all undocumented features.