From TDN

Here are some Markup tags from this post also found here already: GUI/TorqueML

\n - new line
\t - tab stop
<font: > - sample use: "<font:DomCasualD:28>Foo" 
<tag: >
<color:rrggbb> - red green blue in hex format
<linkcolor: >
<linkcolorhl: >
<bitmap: >
<spush> - saves current text format
<spop> - restores text format that was pushed
<sbreak>
<just:left> - left justification
<just:right> - right justtification
<just:center> - centers text
<lmargin%: >
<lmargin: >
<rmargin%: >
<rmargin: >
<clip: >
<div: >
<tab: > - set tab stops?
<a:>
</a>

I also added a couple of new tags that I found useful:

<colora:rrggbbaa> - sets alpha channel along with color
<u> - start underlining text
</u> - stop underlining