code: function isAncestorIDOf(ancestorID, descendantID) {
    return (
      descendantID.indexOf(ancestorID) === 0 &&
      isBoundary(descendantID, ancestorID.length)
    );
  }
docs: Checks if the first ID is an ancestor of or equal to the second ID.
  
  @param {string} ancestorID
  @param {string} descendantID
  @return {boolean} True if `ancestorID` is an ancestor of `descendantID`.
  @internal