Yeah, I figured it out through trial and error. It appears to match entire header lines by regular expression, so I had to write rules like:
[Headers] [contains] [List-Id:.*lists.mozilla.org]
When I say “header name” vs. “header value”, I’m referring to the way headers are treated according to the RFCs:
"Header fields are lines composed of a field name, followed by a colon (":"), followed by a field body"
So an email header like:
List-Id: "For discussions about how to grow Mozilla and bring in new
contributors. " <mozillians.lists.mozilla.org>
“List-Id” is the header name, and the value is everything after the colon. Most desktop e-mail clients will allow you to filter on arbitrary header values, like [List-Id] [contains] [lists.mozilla.org].