non-space character must follow the leading markup
          </li>
<li class="listitem">
            A non-space character must precede the trailing markup
          </li>
<li class="listitem">
            A space or a punctuation must follow the trailing markup
          </li>
<li class="listitem">
            If the matching markup cannot be found within a block, the formatting
            will not be applied. This is to ensure that un-matched formatting markups,
            which can be a common mistake,