Very basic asciidoctor-latex toolchain with pre and post processor,
block processor, latex backend, and one addition html5 template
in place.  The toolchain can now handle the "environment block"

   [env.theorem]

with either the html or latex backend. Note that the second
element of the environment block is variable and not defined
in advance.  Thus one has the usual [env.proposition],
[env.definition], [env.lemma], etc, but also [env.joke],
[env.prayer] ... whatever you need.