function test_props( props, callback ) {
        for ( var i in props ) {
            if ( m_style[ props[i] ] !== undefined && ( !callback || callback( props[i], m ) ) ) {
                return true;
            }
        }
    }
test_props is a generic CSS / DOM property test; if a browser supports
  a certain property, it won't return undefined for it.
  A supported CSS property returns empty string when its not yet set.