Returns a list of encodings in Content-Encoding field as an array of
strings.
The encodings are downcased for canonicalization.
# File lib/open-uri.rb, line 565
def content_encoding
vs = @metas['content-encoding']
if vs && %{\A#{RE_LWS}?#{RE_TOKEN}#{RE_LWS}?(?:,#{RE_LWS}?#{RE_TOKEN}#{RE_LWS}?)*} =~ (v = vs.join(', '))
v.scan(RE_TOKEN).map {|content_coding| content_coding.downcase}
else
[]
end
end