implement .clone, .slice, and yxml.get

src/types/YText.js

@@ -762,6 +762,15 @@ export class YText extends AbstractType {
     return new YText()
   }
 
+  /**
+   * @return {YText}
+   */
+  clone () {
+    const text = new YText()
+    text.applyDelta(this.toDelta())
+    return text
+  }
+
   /**
    * Creates YTextEvent and calls observers.
    *