Steemit's HTML Whitelist

Steemit posts support a limited subset of HTML that can be mixed with the Markdown syntax.
While Markdown is documented (click on 'Markdown Styling Guide' in the editor view), I was not able to find any detailed documentation for HTML in Steemit posts.
I thought that I could do it myself and gathered the information from the source code of Condenser, the official Steemit UI.
This following list of tags, attributes and classes is my interpretation of the code. I hope it helps. Please keep in mind that this is not officially documented and Steemit may change the whitelitsted HTML in the future. Also, please let me know in the comments if you find any mistakes or missing information.

Tags that allow attributes

• a (Reference)
  • Attributes
    • href
    • rel
• div (Reference)
  • Attributes
    • class
      • Allowed class values
        • pull-right
        • pull-left
        • text-justify
        • text-rtl
        • text-center
        • text-right
        • videoWrapper
        • phishy
    • title
• iframe (Reference)
  • Attributes
    • src
      • Supports only youtube, vimeo and soundcloud
    • width
    • height
    • frameborder
    • allowfullscreen
    • webkitallowfullscreen
    • mozallowfullscreen
• img (Reference)
  • Attributes
    • src
    • alt
• td (Reference)
  • Attributes
    • style

Tags without attributes

• b (Reference)
• blockquote (Reference)
• br (Reference)
• center (Reference)
• code (Reference)
• del (Reference)
• em (Reference)
• h1 (Reference)
• h2 (Reference)
• h3 (Reference)
• h4 (Reference)
• h5 (Reference)
• h6 (Reference)
• hr (Reference)
• i (Reference)
• li (Reference)
• ol (Reference)
• p (Reference)
• pre (Reference)
• q (Reference)
• strike (Reference)
• strong (Reference)
• sub (Reference)
• sup (Reference)
• table (Reference)
• tbody (Reference)
• th (Reference)
• thead (Reference)
• tr (Reference)
• ul (Reference)

Furthermore, HTML entities like   are allowed.

As @dbooster pointed out, Steemit removes HTML comments from the markup. Besides of obscure Markdown voodoo, there seems to be no good way to have comments in articles.

Based on this information, I am happy to be able to offer you this helpful snippet:

<center>
<div class="phishy">&#128293;&#128293;&#128293;UPVOTERS ARE MORE SUCCESSFUL&#128293;&#128293;&#128293;</div><br>
<div class="phishy">&#128293;&#128293;&#128293;RESTEEMERS LIVE LONGER&#128293;&#128293;&#128293;</div>
</center>

It should produce following output: