@Override
    public int size() {
        return content.size();
    }
This is an encapsulation of the header fields that belong to either a {@link Request} or a {@link Response}. It is
a multimap from String to String, with some additional methods for convenience. The keys of this map are compared by
ignoring their case, so that <code>get("foo")</code> returns the same entry as <code>get("FOO")</code>.

@author Simon Thoresen Hult
jdisc_core/src/main/java/com/yahoo/jdisc/HeaderFields.java