How are those non-standard HTML tags supposed to work?

Can someone help me to make sense of this?

https://github.com/bigskysoftware/contact-app/blob/6b9449c93e67b4f2526763bd3e91700b3023f455/templates/layout.html#L16-L17

I cannot figure out what this is and how it's supposed to work. It's not standard HTML tags, so what is it?

It also doesn't seem to do quite what it is implying to do. Like, the content of the `` tag is not rendered in all caps when I try it.

Start with templates/layout.html at lines 16–17 and trace where the non-standard tags are handled in the project. Check the existing documentation and relevant source entry points to determine how the tags work and whether the all-caps behavior is intended. Done means documenting the mechanism and clarifying the expected behavior of .

Written by the indexing model from the issue text.