I've committed [a69ad2fd43], the forgotten cases with justifying "right" and "center" has been added.

> c) After removal of a tag with -tabs, it cannot be re-applied.

This is a little bug in your test script, you have to use "remove" instead of "delete" for removing tags from text. Unfortunately it's not easy to detect this kind of bug, because "delete" also excepts any number of arguments, and does not complain about unknown tags.