The weight of each vertex in a vertex group defines how much it is influenced by the bone associated with that group.
Armature weight painting successfully completed. Testing to see if updated mesh and armature works in game environment.
Not using Three.js Blender exporter's Morph Animation option, which generates 100+ MB files. Just going to create a mesh for each shape key (i.e. blink, mouth open), which can then be blended with the basis mesh by the game engine.