Documentation for "alternate full address" setting in .rdp files

Windows Remote Desktop Connection (mstsc) saves the remote computer name like this:

full address:s:rdsh1.whatever.microsoft.com

But if mstsc is launched via Remote Desktop Web Access, the used rdp files have the following content:

full address:s:rdsh1.whatever.microsoft.com
alternate full address:s:rdsh1.whatever.microsoft.com

If an rdp file contains "alternate full address" then "full address" seems to be ignored completely, even if "alternate full address" cannot be resolved.

What is "alternate full address", what is the difference to "full address" and where is the documentation for these settings?

Thanks for any hints!

Note:
https://docs.microsoft.com/en-us/windows/desktop/api/rdpappcontainerclient/nf-rdpappcontainerclient-iremotedesktopclientsettings-setrdpproperty is not helping since that documentation merely converts the setting name into a sentence ;)