code: function _validateFrame(state, frame) {
    if(!_isArray(frame) || frame.length !== 1 || !_isObject(frame[0])) {
      throw new JsonLdError(
        'Invalid JSON-LD syntax; a JSON-LD frame must be a single object.',
        'jsonld.SyntaxError', {frame: frame});
    }
  }
docs: Validates a JSON-LD frame, throwing an exception if the frame is invalid.
  
  @param state the current frame state.
  @param frame the frame to validate.