linguisticsgirl.com: ... In my mind, grammatical *form**(what a word looks like) is clearly separate from grammatical function (what a word does). From ODO: 2.1. Any of the ways in which a word may be spelled, pronounced, or inflected 4.2. [count noun] A set order of words; a formula:
When Michael J. Fox played 'Johnny B. Goode' as Marty McFly in 'Back to the Future' in 1985, he was just aping Chuck Berry's classic fretwork for the camera. (Along with some Jimi Hendrix, Eddie Van Halen and Pete Townsend guitar moves thrown in for good measure.) Today, Fox can really play the song.
In an episode of Back to the Future: The Animated Series, Marty McFly believes he looks like Michael J. Fox, a sort of fourth wall breach or self-reference, however the voice of Marty in the series was not of Fox's, but instead David Kaufman.