How to limit users to use only predefined tags by admin (users not being able to create tags)

Question

I want letting users using only predefined tags and not being able to define new tags themselves

How to go about doing this?

Answer 1

Check the filter module documentation: http://docs.question2answer.org/plugins/modules-filter

You just need to write a plugin with a filter module that implements the filter_question() function and block the creation of the question if there is any non-existent tag.

Taking it a step further you could check the level of a user (admin, registered user, etc) and decide if that user can (or cannot) create tags.