The LoadContentFile method was implemented to support legacy xml files for RadMenu 3.x as shown in the XML Definition online example. Therefore you can use all properties of RadMenu 3.x in addition to all available properties of RadMenu's current Prometheus and classic ASP.NET versions.
Attached is the chm help file of RadMenu 3.7 which you can use for reference of available properties. Also you can refer to Migrating RadMenu Classic to RadMenu Prometheus in the help. You can use either property - Prometheus or classic version.
Our recommendation is to use only properties for RadMenu "Prometheus". All the GroupSettings properties should be in the <group> </group> tags.
If you have any other questions, please, feel free to contact us.