chore: compatible for api def (#423)

Author: zombieJ

src/interface.ts

@@ -29,6 +29,11 @@ export interface AlignType {
    * Point can be 't'(top), 'b'(bottom), 'c'(center), 'l'(left), 'r'(right) */
   points?: (string | AlignPoint)[];
 
+  /**
+   * @private Do not use in your production code
+   */
+  _experimental?: Record<string, any>;
+
   /**
    * offset source node by offset[0] in x and offset[1] in y.
    * If offset contains percentage string value, it is relative to sourceNode region.