xt/html filter (mhtxthtml.pl) will
    disable auto-loaded URL attributes for some HTML elements --
    <tt>IMG</tt>, <tt>BODY</tt>, <tt>IFRAME</tt>, <tt>FRAME</tt>,
    <tt>OBJECT</tt>, <tt>SCRIPT</tt>, <tt>INPUT</tt> -- except for cid:
    URLs.  This behavior can be disabled if the '<tt>allownoncidurls</tt>'
    filter argument is specified.
    </p>
    <p>The new behavior prevents malicious URLs being used to verify
    mail addresses, secretly setting cookies, or
    gather some statistical data witho