Heads-up to all developers, I've just released s9e\TextFormatter v0.7.0 and there's been a small but important change in the API. Specifically, setSortPriority() is deprecated and will emit a E_USER_DEPRECATED warning when called. The method will be removed at some point in the future.
If you don't use setSortPriority(), you are unaffected and you don't have to read further.
From now on, instead of this: (s9e\TextFormatter 0.6.2 and earlier)
$parser->addStartTag($name, $pos, $len)->setSortPriority($prio);
...you will have to use this: (s9e\TextFormatter 0.7.0)
$parser->addStartTag($name, $pos, $len, $prio);
All other related methods accept an additional argument as well. If you don't know which version your code will use, you can use this as a stopgap measure:
@$parser->addStartTag($name, $pos, $len, $prio)->setSortPriority($prio);
As soon as Flarum's dependencies are updated, I recommend that you update your own dependencies to require the latest version of Flarum and remove all calls to setSortPriority().
Pinging @Toby @Franz @jordanjay29 and @luceos in case someone was thinking about bumping the requirement for Beta 6.