code: function compare(pathA, pathB) {
    pathA = pathA.split(sep);
    pathB = pathB.split('/');
    if (!pathA[pathA.length - 1]) pathA.pop();
    if (!pathB[0]) pathB.shift();
    var overlap = [];
  
    while (pathA[pathA.length - 1] == pathB[0]) {
      overlap.push(pathA.pop());
      pathB.shift();
    }
    return overlap.join('/');
  }
docs: get the overlaping path from the end of path A, and the begining of path B.
  
  @param {String} pathA
  @param {String} pathB
  @return {String}
  @api private