code: public void dropAttribute(int semantics) {
  		_touch();
  		if (!m_description.hasAttribute(semantics))
  			return;
  
  		VertexDescription newvd = VertexDescriptionDesignerImpl.removeSemanticsFromVertexDescription(m_description, semantics);
  		_assignVertexDescriptionImpl(newvd);
  	}
docs: Drops an attribute from the Geometry. Dropping the attribute is
  equivalent to setting the attribute to the default value for each vertex,
  However, it is faster and the result Geometry has smaller memory
  footprint and smaller size when persisted.
  @param semantics The VertexDescription.Semantics to drop.