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}
function isMeta(expression, value = null) {
  return expression.type === 'Char' &&
    expression.kind === 'meta' &&
    (value ? expression.value === value : /^\\[dws]$/i.test(expression.value));
}