\IM{nonexist3} Logical impossibilities
+Fingly \i{eep}.
+
+\IM{eep} Thing: with a colon
+
+Flongly \i{eep:sping}.
+
\define{macro} macro definition
\define{macro} same macro again
Unclosed brace: \c{foo.
+\U Spong, wimble: flomp.
+
Comment to EOF: \#{ and here we go.