RotulusMark

An opaque handle to a row. A mark stays valid until the row it names goes (removed, trimmed by RotulusView:max-lines, or cleared), and is weak: using a stale one is a safe no-op, and rotulus_view_remove() returning FALSE is the intended way to find out.

A mark is an id rather than a pointer to anything. It is a boxed type so that language bindings can hold one, but copying it returns the same mark and freeing it does nothing, so C code never needs to.