From https://xpra.org/trac/browser/xpra/trunk/src/html5/index.html#L115
For more information, see <a href="https://xpra.org/trac/wiki/HTML5">xpra HTML5 wiki</a>.
This link is dead. The correct link is https://xpra.org/trac/wiki/Clients/HTML5.
Many thanks, applied in r22125.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2220