Comments

In ASCEND syntax, comments can be written within the special delimiters (* and *). Comments can be nested (note that in some text-editors, this can confuse the syntax highlighting, but it still works fine in ASCEND)

Example:

(*
    This model is very useless, because it doesn't have
    any equations in it yet.
*)
MODEL mymodel;
    d IS_A distance; (* pipe diameter *)
END mymodel;