A Displacement modifier is doing a great job making a mesh look a realistic object, but there are certain spots, such as a dozen or so vertices at one corner of the mesh, where I don't want any displacement effect. The displacment is making a mess of things in those spots.
I don't want to undo my brilliant sculpting work there and re-do it after applying the modifier, or to fix the mess afterward. In fact, I don't want to apply the modifier. Never mind my particular reason, since other Blender modelers may have the same question and want to animate, adjust the Displacment settings later, copy the object but have different ripples in the objects (using global coords), or whatever.
What would be nice is a way to modulate the "strength" setting with a grayscale image or painting in a UV map, but I'm not seeing how to do that. I'm one of: unlucky at Google today, stupid, or ignorant of some non-obvious feature in Blender. Maybe there's a nodes editor way to build a processing pipeline for modifier parameters?