code: function isMeta(expression, value = null) {
    return expression.type === 'Char' &&
      expression.kind === 'meta' &&
      (value ? expression.value === value : /^\\[dws]$/i.test(expression.value));
  }
docs: Checks if a node is a meta char from the set \d\w\s\D\W\S
  @param {Object} expression - Char or ClassRange node
  @param {?string} value
  @returns {boolean}