code: function normalizeHeaderKey() {
    var key = arguments.length > 0 && arguments[0] !== undefined ? arguments[0] : '';
  
    return key.replace(/\r?\n|\r/g, ' ') // no newlines in keys
    .trim().toLowerCase().replace(/^MIME\b|^[a-z]|-[a-z]/ig, function (c) {
      return c.toUpperCase();
    }); // use uppercase words, except MIME
  }
docs: Normalizes a header key, uses Camel-Case form, except for uppercase MIME-
  
  @param {String} key Key to be normalized
  @return {String} key in Camel-Case form