Add Facets/Vertices to Selection Set via script?

I'm wondering what the command is to add a specific facet (or vertex) to a Selection Set?

I know addSelectedFacetsToGroup("[group name]") works only if I have previously selected geometry in the viewport. I want a way where I bypass that and add certain facets to a group without having to select them in the viewport. A workaround would be to make a selection of a facet via script but I don't know how to do that either. I tried the getFacet() command but when used with the addSelectedFacetsToGroup() it does nothing.