text: 'use strict';
  
  // See https://www.ampproject.org/docs/reference/validation_errors
  
  const disallowedAtRules = new Set([
    'charset',
    'import',
    'namespace',
    'document',
    'viewport',
    '-ms-viewport'
  ]);
  
  function removeDisallowedAtRules(root) {
    root.walkAtRules(rule => {
      if (disallowedAtRules.has(rule.name)) {
        rule.remove();
      }
    });
  }
  
  module.exports = removeDisallowedAtRules;
  