docs: function sn_ui_pixelWidth(selector) {
  	if ( selector === undefined ) {
  		return undefined;
  	}
  	var styleWidth = d3.select(selector).style('width');
  	if ( !styleWidth ) {
  		return null;
  	}
  	var pixels = styleWidth.match(/([0-9.]+)px/);
  	if ( pixels === null ) {
  		return null;
  	}
  	var result = Math.floor(pixels[1]);
  	if ( isNaN(result) ) {
  		return null;
  	}
  	return result;
  }