I find the pre-supplied list of selection rules to create panel variants to be quite lacking. For instance, if I am using panels to override taxonomy term pages, and I have some arbitrary boolean field on each term (say, "Is Blog?"), then I would like to create a panel variant based on this field being equal to TRUE.
However there is no such flexibility when using Selection Rules to create variants. Am I alone in thinking that this missing functionality greatly diminishes the power of Panels and panel variants?
How would a site builder, or developer, go about creating new "custom" selection rules?