Supported:

<p>, <span>, <strong>, <b>, <i>, <em>, <br>

Supported tags with attributes:

<a href="URL">
<img src="URL" alt="description">

Supported by some:

<div>, <h1>, <h2>, <h3>, <h4>, <h5>, <h6>, <span style="color:red">

Not supported:

<iframe>, <script>, <div>, <style>