In testing for bug 945 (validation of SVG path data) with long attribute values that contain line breaks, Simon pointed out that the literal newlines show up as-is in the "Bad value `...` for attribute" message that gets emitted -- so that the message ends up getting broken up into multiple lines, making it ugly and hard to read.

<zcorpan> MikeSmith: i found a different bug now. newlines in the attribute value get shown as literal newlines in the message (both for "bad value `...`" and the new context)
 <zcorpan> MikeSmith: maybe they should be replaced with ↩

The gnu and json output formats already do replacement of newlines with "↩". It'd be good to do the same thing for HTML output.

I hacked a fix into the MessageEmitterAdapter code in my working directory but the right place to change it is in the XhtmlMessageTextHandler code.