This plugin consist of 2 plugins (Mask Top and mask Bottom) that allow you to mask the effect of modifier based on a bitmap or material. The normal usages is to create an object with texture mapping coords. Apply the Mask Bottom, then apply some sort of modifier (Note this modifier cannot change the face or vertex count so you could NOT use Meshsmooth or Tesselate etc.), then apply the Mask Top. Create a bitmap or material that you want to use as a mask and pick it. Your stack should look something like below.