Bundled services interpretation: tax the bundle by its essential character or by the element creating highest liability. Section 66F establishes that a main service does not include services used to provide it, that specific descriptions prevail over general ones, and that bundled services are taxed either as the single service giving the bundle its essential character when elements are naturally bundled, or as the service producing the highest tax liability when they are not. Natural bundling is a facts-and-circumstances inquiry relying on indicia like component cost and functionality.