/// <summary>
/// Marks the given element with the given color.
/// </summary>
public void MarkElement( HtmlElement e, Color color )
{
e.Require( x => e != null );
if ( IsMarked( e ) )
{
// unmark first - maybe it was marked with another color before
UnmarkElement( e );
}
e.MarkElement( color );
MarkedElements.Add( e );
}
