The SelectableCorona is an abstract corona, i.e. it can not be directly used in your scenario, however, it implements common functionality used by coronas which can be selected.
Selectable coronas keep track of a selection state and change their appearance accordingly.
The mandatory numeric <index> property allows differentiating multiple selectable coronas if more than one such corona is associated with a handle. Specified value MUST be an integer value.
The optional <selected> flag allows pre-selecting selectable coronas in a scenario. If omitted, the flag defaults to false.
The optional <group> property allows grouping multiple selectable coronas inside a named group. All selectable coronas to be grouped shall specify the same name for their respective <group> property.
Most selectable coronas have multiple colour properties controlling their appearance. As already mentioned earlier, selectable coronas keep track of their selection state and can be either in selected or deselected state. To allow the specification of state dependent colours, selectable coronas rely on so called Colour Pairs for the definition of their colour properties. A Colour Pair distinguishes between a <selected> colour and a <deselected>colour.