private void outputHighlight(final StringBuilder output) {
        if (changedHighlight) {
            if (inHighlight) {
                // Output a highlight if we are in a highlight section.
                write(Style.HIGHLIGHT.getStart());
            } else {
                // We are moving out of the highlight state so output an end
                // span.
                write(Style.HIGHLIGHT.getEnd());
            }
        }
    }
Outputs the appropriate highlight start or end element depending on
whether we are switching to or from the highlight state.

@param output The output <code>StringBuilder</code> to append the highlight
              element to.
stroom-core-client-widget/src/main/java/stroom/editor/client/model/XMLStyler.java