All of these features are essentially trivial variations on each other. They should all be relatively simple to create as variations of "Make it an Amplet", where the selected text is replaced by a suitable DOM node whose contents are the selected text.
OK, we have everything except right/left justification. Also, some of these (center, strikethrough) don't work as toggles like the rest, so need some more debugging.
All of these features are essentially trivial variations on each other. They should all be relatively simple to create as variations of "Make it an Amplet", where the selected text is replaced by a suitable DOM node whose contents are the selected text.