function isAncestorIDOf(ancestorID, descendantID) {
  return descendantID.indexOf(ancestorID) === 0 && isBoundary(descendantID, ancestorID.length);
}
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