[Exim] Plus extension not in FAQ?

Hi folks,

Am I being obtuse, or is the fairly frequently required "plus extension"
not covered in the FAQ? I found sample configuration C010, but it's
horribly complicated. I had to figure this director out for myself:

# This director allows localpart+arbitrary_extension@??? style
# addresses.
#
# If you don't have a LOCAL_DOMAINS macro defined, replace it with
# your list of local domains.
#
plus_extension:
domains = LOCAL_DOMAINS
local_parts = ^.+\\+.+
driver = smartuser
new_address = ${extract{1}{+}{${local_part}}}@${domain}

If I'm _not_ being obtuse, can I suggest its inclusion in the FAQ?
Perhaps as an answer to:

    How do I configure Exim to allow arbitrary extensions in local
    localparts, of the form "+extension"?

Ciao,
Sheldon.