Search is fulltext search and SQL wildcards as "_", "%'', are therefore not needed.
Since Mendix does not perform properly on wildcards as "!", and "*", I think Mendix does not use SQL wildcards, but substitutes characters like "_" and "%''.
I am not sure whether your answer is right.
The same wildcards as SQL, so that would mean "%" and "*", if I'm not mistaken.
And another tip is what to do when you want to search for "_" for instance. You can escape the character with a "\". So "\_" will find all the underscores in your search.
Would be great to use operator > < as well!
This would allow you to search on greater then or smaller then or even reaches.