extend(e) {
    var t = {
      style: this.style,
      size: this.size,
      textSize: this.textSize,
      color: this.color,
      phantom: this.phantom,
      font: this.font,
      fontFamily: this.fontFamily,
      fontWeight: this.fontWeight,
      fontShape: this.fontShape,
      maxSize: this.maxSize,
      minRuleThickness: this.minRuleThickness
    };
    for (var r in e)
      e.hasOwnProperty(r) && (t[r] = e[r]);
    return new Dr(t);
  }
Returns a new options object with the same properties as "this".  Properties
from "extension" will be copied to the new options object.