Full Idea
I think modality has to do with relations involving the abstract part of the world, specifically with relations among (Platonic) properties.
Gist of Idea
Modality concerns relations among platonic properties
Source
Michael Jubien (Possibility [2009], 3.2)
Book Reference
Jubien,Michael: 'Possibility' [OUP 2009], p.77
A Reaction
[Sider calls Jubien's the 'governance' view, since abstract relations govern the concrete] I take Jubien here (having done a beautiful demolition job on the possible worlds account of modality) to go spectacularly wrong. Modality starts in the concrete.