It seems that the strings in the _ attribute aren't actually being read at runtime. E.g. if you edit them in the DOM it doesn't change anything. I assume this means it's compiled once on DOM load?
If you'd like to play around, open the console and try calling the `_hyperscript` function:
_hyperscript(`get the first <button/>
transition its background-color to 'red' over 2s
log ':]'
`)https://hyperscript.org/playground/
Still a work in progress, but you can play around w/ the language.