Specifies whether to render embedded HTML. If checked, many of HTML markup will be rendered with the appropriate features of RTF.

As for now, the supported HTML tags are the following:
Text <b>, <strong>, <i>, <em>, <code>, <tt>, <u>, <s>, <strike>, <sub>, <sup>, <font>, <br>
Paragraphs <p>, <center>, <div>, <pre>, <h1>, <h2>, <h3>, <h4>, <h5>, <h6>, <blockquote>
Lists <ul>, <ol>, <li>, <dl>, <dt>, <dd>
Table <table>, <tr>, <td>, <th>
Other <hr>, <img>, <a>...</a>

Note: This setting affects only output of those template components whose 'Render embedded HTML' option is checked. This option is located at the component's Properties Dialog | Formatting | Text Flow tab. When such an option is not specified, any markup contained in the component's output will be treated as an ordinary text.