Etiquette

This is the readme file.

Make the wording between "new", "create", "add" and "remove", "delete" more consistent.
At the moment I don't like the way that warnings and exceptions are so far apart, and need to be updated individually. Consider moving the warning strings to be class properties of the matching exceptions.
User account system, permission levels, private pages.
Generalize the filename expression filter so it can work with any strings.
Improve the "tags on this page" list. Maybe add separate buttons for must/may/forbid on each.
Some way for the database to re-identify a file that was moved / renamed (lost & found). Maybe file hash of the first few mb is good enough.
Move out more helpers
Debate whether the UserMixin.login method should accept usernames or I should standardize the usage of IDs only internally.

[addition] A new feature was added.
[bugfix] Incorrect behavior was fixed.
[change] An existing feature was slightly modified or parameters were renamed.
[cleanup] Code was improved, comments were added, or other changes with minor impact on the interface.
[removal] An old feature was removed.