* means corrected

1) Additional element of a block can hide a cursor.
2)* If part of long hierarchy of radicals disappears on the right,
anything disappears. (* Was: wrong interaction of wrapped lines with
tcl layout. *)
3) Algorithm for layout can become exponential if it tries to wrap
around n levels of IBTrees to fit into space.
4) Change ArgAppendCopy to ArgAppendShadow? (incr refcount instead of copy?)