html_tidy(commandline, what)

Passes the the specified commandline to tidy the string what.

To make this work, tidy obviously has to be present on your system. If not see http://tidy.sourceforge.net/ for details

There are zillions of options tidy supports, this may be confusing to some, so here is a sample commandline that may be sufficient:

commandline = 'path/to/tidy/tidy --indent yes'