or a one-character string, it is added to the mode's syntax table with
`comment-start' syntax. If the entry is a cons pair, the elements of the
pair are considered to be `comment-start' and `comment-end' respectively.
+\(The latter should be nil if you want comments to end at end of line.)
Note that Emacs has limitations regarding comment characters.
KEYWORD-LIST is a list of keywords to highlight with `font-lock-keyword-face'.