code: function(expectedSignature) {
          var signature = this.reader.readString(4);
          if (signature !== expectedSignature) {
              throw new Error("Corrupted zip or bug : unexpected signature " + "(" + utils.pretty(signature) + ", expected " + utils.pretty(expectedSignature) + ")");
          }
      }
docs: Check that the reader is on the speficied signature.
  @param {string} expectedSignature the expected signature.
  @throws {Error} if it is an other signature.