code: function createRegExp (regexp, options) {
      return new DuckType({
        name: options && options.name || null,
        test: function (object) {
          return ((object instanceof String) || typeof(object) === 'string') && regexp.test(object);
        }
      });
    }
docs: Create a ducktype from a regular expression. The created ducktype
  will check whether the provided object is a String,
  and matches with the regular expression
  @param {RegExp} regexp   A regular expression
  @param {{name: String}} [options]
  @returns {*}