By RFC 1123, underscores are not permitted in host names.
(This is in contrast to the specification for DNS, RFC
2181, which allows underscores.)
However, most browsers do the right thing when faced with
an underscore in the host name, and so some poorly written
websites are written with the expectation this should work.
Setting this parameter to true relaxes our allowed character
check so that underscores are permitted.
--# vim: et sw=4 sts=4