Having
latexrender available, one can edit the _class.latexrender.php_ file
to include additional LaTeX-packages. For example adding the lines
string .= '\usepackage{xy}\n';
string .= '\xyoption{all}\n';
string .= '\newcommand{\vtx}[1]{*+[o][F-]{\scriptscriptstyle #1}}\n';
makes it possible to include quiver-pictures in this weblog.
Observe the double blackslash before newcommand, a single backslash
would produce a new-line and fail to define something.