* HTML_reactive: Cosmetics.
* HTML_reactive: Cosmetics.
* CORE_client_reaction:
  Stronger typing of client's reactions. The only way to build a
  client reaction is to wrap a function using install_client_reaction.

* HTML_reactive:
  Use the [reaction] abstract type.
* HTML_autotest:
  Annotate client code fragment with [reaction] instead of [unit].
* Web interface, still a draft, yet less ugly.