It is theoretically possible to program in HTML and CSS, but in
practice this capability is limited and inconvenient; merely to
make it do something is an impressive hack.
So I echo der.hans and ask again: HTML5 as JS? Is this a thing now?!
I do NOT ask "Can we expect w3.org to keep these things off us?"
because I don't want to sound like a serf. I dare ask "Can we pepper
our banks and grocery stores with requests that appear to come from
browsers that do not support HTML5 nor JS?" and I ask this because I
expect the free market to listen like no leet standards body flogging
a dead mandate.
[Brought to you by Honest To Goodness text/plain.]