Add comments throughout file. (#2480)
Add comments throughout file. (#2480)

* Add comments throughout file.

* Add doxygen @code and \p.

* Replace incorrect comment.

billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake,billhoffman/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,sheim/drake,billhoffman/drake,billhoffman/drake,billhoffman/drake,sheim/drake,billhoffman/drake