code: function normalizeRel(base, input) {
    if (!input) return;
    if (!Array.isArray(input)) input = [ input ];
  
    return flatten(input).map(function (rel) {
      return rel in iana ? rel : url.resolve(base, rel);
    });
  }
docs: Takes the `input` rel value and normalizes it into a valid array.
  
  @param {String} base  The base URL for this API.
  @param {Mixed} input  The rel value to normalize.
  @return {Array}