optionally

from WordNet (r) 3.0 (2006)
optionally
    adv 1: in an optional manner; "this rule is applied optionally"
           [ant: {obligatorily}]
from The Collaborative International Dictionary of English v.0.48
Optionally \Op"tion*al*ly\, adv.
   In an optional manner.
   [1913 Webster]
antiflux / dictionary / optionally
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