Why is this not using :set ft=html.jinja

[SirVer]

I think your plugin duplicates some efforts that Vim already contains, namely dotted filetypes. Especially why do you need a new filetype and not use ft=html.jinja?

http://vimdoc.sourceforge.net/htmldoc/options.html#'filetype'

This is in relation to SirVer/ultisnips#137. Could you please have a look and comment there and here?