DTD, Ctrl-D, proper indentation/highlighting

While setting/changing the DTD for an open file is easy in Quanta, I
haven't been able to find a simple menu option (or better, a keyboard
shortcut) that just adds the current DTD string as text in a file being
edited.

Similarly, I haven't been able to find the location of the Ctrl-D
shortcut (turn line into comment). I'd like to define a counterpart (if
possible at all) that removes comment tags.

Lastly, a little nuisance I hope to find a fix for: when creating a new
file, only after saving it as (e.g) .php file can Quanta know what
indentation/highlinghting to apply. But (why) do I have to close and
reopen a file first before Quanta follows the extension's settings?

Regards,
Sh.