old_contents: const cheerio = require('cheerio');
  const nunjucksIncludeData = require('nunjucks-includeData');
  const marky = require('marky-markdown');
  const nunjucksMarkdown = require('nunjucks-markdown');
  
  const replaceEverythingBeforeH2Element = true;
  
  const cleanSlug = slug => slug.replace('setup-instructions', 'setup');
  
  module.exports = function (nunjucksEnv) {
    nunjucksIncludeData.install(nunjucksEnv);
  
    nunjucksMarkdown.register(nunjucksEnv, str => {
      let dirty = marky(str, {
        headingSvgClass: [],
        prefixHeadingIds: false,
        enableHeadingLinkIcons: false
      });
  
      // Remove everything before the first `<h2>` element.
      if (replaceEverythingBeforeH2Element) {
        dirty = dirty.substring(dirty.indexOf('<h2'));
      }
  
      const $ = cheerio.load(dirty);
  
      $('ol, ul').each((idx, list) => {
        const $list = $(list);
        $list.addClass('bullets-light');
        $list.html($list.html().replace(/<li>/gi, '<li><span>').replace(/<\/li>/gi, '</span></li>'));
      });
  
      let html = '';
      let sections = [];
  
      $('h2 > a').each((idx, a) => {
        const $a = $(a);
        const id = cleanSlug($a.attr('id'));
        const href = cleanSlug($a.attr('href'));
        $a.attr('id', id);
        $a.attr('href', href);
        const $h2 = $a.parent();
        const headingText = $h2.text();
        $a.text(headingText);
        $h2.html($a);
  
        if (!html) {
          const bodyHtml = $('body').html();
          html = bodyHtml.substring(0, bodyHtml.indexOf('<h2'));
        }
  
        let sectionHtml = `<section data-section="${id}" id="${id}" class="section">\n`;
        sectionHtml += `${$.html($h2)}\n`;
        $h2.nextUntil('h2').each((idx, sibling) => {
          const $sibling = $(sibling);
          sectionHtml += $.html($sibling) + '\n';
          $sibling.remove();
        });
        sectionHtml += '</section>\n';
  
        sections.push(sectionHtml);
      });
  
      if (sections.length) {
        html += sections.join('\n\n');
      } else {
        html = $('body').html();
      }
  
      return html;
    });
  };
  
new_contents: const cheerio = require('cheerio');
  const nunjucksIncludeData = require('nunjucks-includeData');
  const marky = require('marky-markdown');
  const nunjucksMarkdown = require('nunjucks-markdown');
  
  const stripEverythingBeforeH2Element = true;
  
  const cleanSlug = slug => slug.replace('setup-instructions', 'setup');
  
  module.exports = function (nunjucksEnv) {
    nunjucksIncludeData.install(nunjucksEnv);
  
    nunjucksMarkdown.register(nunjucksEnv, str => {
      let dirty = marky(str, {
        headingSvgClass: [],
        prefixHeadingIds: false,
        enableHeadingLinkIcons: false
      });
  
      // Remove everything before the first `<h2>` element.
      if (stripEverythingBeforeH2Element) {
        dirty = dirty.substring(dirty.indexOf('<h2'));
      }
  
      const $ = cheerio.load(dirty);
  
      $('ol, ul').each((idx, list) => {
        const $list = $(list);
        $list.addClass('bullets-light');
        $list.html($list.html().replace(/<li>/gi, '<li><span>').replace(/<\/li>/gi, '</span></li>'));
      });
  
      let html = '';
      let sections = [];
  
      $('h2 > a').each((idx, a) => {
        const $a = $(a);
        const id = cleanSlug($a.attr('id'));
        const href = cleanSlug($a.attr('href'));
        $a.attr('id', id);
        $a.attr('href', href);
        const $h2 = $a.parent();
        const headingText = $h2.text();
        $a.text(headingText);
        $h2.html($a);
  
        if (!html) {
          const bodyHtml = $('body').html();
          html = bodyHtml.substring(0, bodyHtml.indexOf('<h2'));
        }
  
        let sectionHtml = `<section data-section="${id}" id="${id}" class="section">\n`;
        sectionHtml += `${$.html($h2)}\n`;
        $h2.nextUntil('h2').each((idx, sibling) => {
          const $sibling = $(sibling);
          sectionHtml += $.html($sibling) + '\n';
          $sibling.remove();
        });
        sectionHtml += '</section>\n';
  
        sections.push(sectionHtml);
      });
  
      if (sections.length) {
        html += sections.join('\n\n');
      } else {
        html = $('body').html();
      }
  
      return html;
    });
  };
  
subject: rename variable to `stripEverythingBeforeH2Element`