text: const visit = require('unist-util-visit');
  const toString = require('mdast-util-to-string');
  
  module.exports = function () {
    const highlightRegex = /==(.+?)==/g;
  
    return function (ast) {
      visit(ast, 'text', (node) => {
        const paragraph = toString(node);
  
        if (paragraph.match(highlightRegex)) {
          const html = paragraph.replace(highlightRegex, `<mark className="highlight">$1</mark>`);
  
          node.type = 'html';
          node.children = undefined;
          node.value = html;
        }
      });
    };
  };
  