h %%(include)==heading==%%  => h heading    ;; inline include must correctly deal with block elements.
h %%(include isolate=1)==heading==%% => h heading
h {{include z}} => h <em class="format-error">Cannot {{Include}} z.</em>
h {{include}}   => h <em class="format-error">Cannot inline {{Include}}d document because it only has block elements.</em>


Multiline tests

%%(Include tree=top)
== First level but not -1-th ==
%%
  =>
<h2>
First level but not -1-th
</h2>