Perform basic conversion of instructions markup. This includes
        replacement of several textual markup tags with their HTML equivalents.

        @param soup: BeautifulSoup instance.
        @type soup: BeautifulSoup

def _convert_markup_basic(self, soup):
        """
        Perform basic conversion of instructions markup. This includes
        replacement of several textual markup tags with their HTML equivalents.

        @param soup: BeautifulSoup instance.
        @type soup: BeautifulSoup
        """
        # Inject meta charset tag
        meta = soup.new_tag('meta', charset='UTF-8')
        soup.insert(0, meta)

        # 1. Inject basic CSS style
        css = "".join([
            INSTRUCTIONS_HTML_INJECTION_PRE,
            self._mathjax_cdn_url,
            INSTRUCTIONS_HTML_INJECTION_AFTER])
        css_soup = BeautifulSoup(css)
        soup.append(css_soup)

        # 2. Replace <text> with <p>
        while soup.find('text'):
            soup.find('text').name = 'p'

        # 3. Replace <heading level="1"> with <h1>
        while soup.find('heading'):
            heading = soup.find('heading')
            heading.name = 'h%s' % heading.attrs.get('level', '1')

        # 4. Replace <code> with <pre>
        while soup.find('code'):
            soup.find('code').name = 'pre'

        # 5. Replace <list> with <ol> or <ul>
        while soup.find('list'):
            list_ = soup.find('list')
            type_ = list_.attrs.get('bullettype', 'numbers')
            list_.name = 'ol' if type_ == 'numbers' else 'ul'