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.
Adrienne Barbeau and Barry Bostwick were in the original Broadway cast. John Travolta appeared at some time as a replacement on Broadway in the role of Doody. Marilu Henner, an alumna of the original Chicago production, appeared as a replacement in the role of Marty. Patrick Swayze and Treat Williams were both replacements as Danny Zuko.