node_modules/stylelint/lib/utils/isStandardSyntaxAtRule.js

/* @flow */
"use strict";

/**
 * Check whether a at-rule is standard
 *
 * @param {atRule} postcss at-rule node
 * @return {boolean} If `true`, the declaration is standard
 */
module.exports = function(atRule /*: Object*/) /*: boolean*/ {
  // Ignore scss `@content` inside mixins
  if (!atRule.nodes && atRule.params === "") {
    return false;
  }

  // Ignore Less mixins
  if (atRule.mixin) {
    return false;
  }

  // Ignore Less detached ruleset `@detached-ruleset: { background: red; }; .top { @detached-ruleset(); }`
  if (
    atRule.variable ||
    (!atRule.nodes && atRule.raws.afterName === "" && atRule.params[0] === "(")
  ) {
    return false;
  }

  return true;
};