Last modified: 2014-09-24 00:06:21 UTC
As best I can tell, the four functions in EditPage.php that add messages above the edit window add them in approximately the following order: 1. interface editnotice 2. no-such-user warning 3. Custom editintro supplied by &editintro= GET parameter 4. new-article help 5. log extract for deletion/move logs 6. talk page editnotice 7. Per-namespace editnotices, and per-page editnotices where those are still (accidentally) enabled 8. Edit conflict warning 9. warning you get if you try to create a new section and save it with no text 10. force-edit-summary-warning 11. force-edit-summary-warning for new sections 12. Messages generated by hooks such as Capthas, AbuseFilter, etc 13. warning about browsers that mangle unicode 14. warnings related to RevDelete 15. editing-an-old-revision warning 16. warning about the wiki being locked 17. not-logged-in warning 18. JS warning 19. JS/CSS preview notices 20. warning about semi-protection or full-protection or cascading protection or creation protection 21. long page error or warning A logical order would have the most general notices ([[MediaWiki:readonlywarning]] and then [[Mediawiki:Talkpagetext]]) first, followed by namespace-specific notices (all of which could/should be implemented through the per-namespace editnotice system), followed by per-page editnotices and finally warnings about the particular edit the user is trying to make. And they should be added in a consistent fashion that ensures they are properly parsed, don't get random extra classes added to them, and have consistent ids.
Adding the "design" keyword to get a visual and/or UI designer's help on this.