These text tags are not
Go to Text->SVG Fonts... menu
(but you will just have the menu
if you compile libcairo from git
to see some actual rendering.
rendering properly yet :-(
(try typing strings with the @ and ! characteres on the SVG Fonts dialog!)
before compiling inkscape)
if you are really curious about it, you can look
at the contents of this SVG file in a text editor.
I have put some nice comments there for you!!!!