HEEx is a templating engine on top of Elixir's EEx templating
language specific to HTML that is included in Phoenix.LiveView
(though I think the plan is to eventually include it in base
Phoenix). It's a superset of EEx with some additional features
like components and slots.
The injections don't work perfectly because the Elixir grammar is
newline sensitive (the _terminator rule). See
https://github.com/elixir-lang/tree-sitter-elixir/issues/24
for more information.
Michael Davis