message: allow starting a range with both positions known already
  we'll need this to start a range for the selection
diff: @@ -394,11 +394,12 @@ export default class EditorModel {
  /**
  * Starts a range, which can span across multiple parts, to find and replace text.
  - * @param {DocumentPosition} position where to start the range
  + * @param {DocumentPosition} positionA a boundary of the range
  + * @param {DocumentPosition?} positionB the other boundary of the range, optional
  * @return {Range}
  */
  - startRange(position) {
  - return new Range(this, position);
  + startRange(positionA, positionB = positionA) {
  + return new Range(this, positionA, positionB);
  }
  //mostly internal, called from Range.replace
  