It looks like Google has removed one of their previously documented structured data markups from their developer docs. Specifically, they have removed the Preferred Site Name option, it now 404s when you try to access it, but for now, the cached version is still available.

You were able to use structured data markup on your official website to indicate the preferred name you want Google Search to display in Search results. But they removed the documentation, so does that mean Google will no longer support this markup?

Aaron Bradley first spotted this and posted it on Google+ yesterday saying "looks like "Preferred site name" is no longer supported by Google."

I asked John Mueller about it on Google+, but have not yet heard back if this is just an error or something Google has fully stopped supporting.

Here is a screen shot of the old document:

Forum discussion at Google+.