code: function(marker, width, height, block) {
      var attr = ['marker']
  
      // Build attribute name
      if (marker != 'all') attr.push(marker)
      attr = attr.join('-')
  
      // Set marker attribute
      marker = arguments[1] instanceof SVG.Marker ?
        arguments[1] :
        this.doc().marker(width, height, block)
  
      return this.attr(attr, marker)
    }
docs: Create and attach markers