We have defined a component that accepts drag-and-drop of user content, and the cq:DropTargetConfig node (under cq:editConfig > cq:dropTargets) defines groups=[page] because it accepts assets of type cq:Page not images. Our component is a copy of the /libs/foundation/components/image component, because it accepts drag-and-drop, and we modified its innards to accept cq:Page not image. Seems that the 'accept' property is completely ignored when groups=[page], I think 'accept' is only processed when groups=[media] i.e. images.
This is basically working fine except there is so much user content that it is time-consuming for users to select the right pages to drag from the Content Finder extension into the drag-and-drop target. And if they pick the wrong kind of asset it can really mess up the target page. There are so many types of components based on cq:Page and many of them just do not belong in this particular drop target, but if the user drags an inappropriate asset into our drop target then cq allows it, often with disastrous results (content properties and nodes get overwritten in the wrong place, etc).
Yes the Content Finder has a search bar but really I would like to restrict the list of assets shown there without the user having to type in a search term. I hope there is something for Page-based content analogous to the 'allowedPaths' property in a Template. In the WCM when you click New Page at some jcr path, a template-chooser dialog comes up and it only has templates which are allowed for that jcr path, so the dialog is uncluttered and guides the user to a relevant template. Similarly, Components have an 'allowedParents' property so you can't use them where they don't belong. Please advise if there is something similar to make it easier to find relevant content in Content Finder tab Pages.