# @option     +oa                   
# @option +b  +ob                   short
# @option +c                        short only
# @option     +oc!                  required
# @option     +od*                  multi-occurs
# @option     +oe+                  required + multi-occurs
# @option     +ona <PATH>           value notation
# @option     +onb <CMD> <FILE>     two-args value notations
# @option     +onc <CMD> <FILE+>    unlimited-args value notations
# @option     +oda=a                default
# @option     +odb=`_default_fn`    default from fn
# @option     +oca[a|b]             choice
# @option     +ocb[=a|b]            choice + default
# @option     +occ*[a|b]            multi-occurs + choice
# @option     +ocd+[a|b]            required + multi-occurs + choice
# @option     +ofa[`_choice_fn`]    choice from fn
# @option     +ofb[?`_choice_fn`]   choice from fn + no validation
# @option     +ofc*[`_choice_fn`]   multi-occurs + choice from fn
# @option     +oxa~                 capture all remaining args

# @option +b  -ob
# @option +c --oc
# @option -d  +od