Users search box treats underscores as wildcards, not as characters

Question

The underscore _ is a valid character in user names, but when searching users on stackoverflow.com/users, it is treated as a wildcard(!), not as a character. For example, when I type w_of__ in the search box, then not only the user shadow_of__soul appears in the search results, but also, e.g, BiscutWoofington. The user Wooff is not shown, which makes sense since it's only 5 characters long and thus doesn't match the pattern w?of??.

This leads me to the following questions:

1. Is the above behaviour a bug or status-bydesign?
2. Shouldn't _ be treated as a normal character, and ? be used as a wildcard instead?
3. What characters other than letters and digits are allowed in user names? So far I found spaces and . - ' _.

(Some testing indicates that underscores are treated just like letters and digits in comment notifications.)

Answer 1

We allow the following regex in search: \w' \.\- there was minor oversight that meant I did not disable the _ wildcard that is passed in to the search LIKE clause.

I fixed that, it is way too non-intuitive to find. So now, there are no more wildcards for username search.

I dislike the idea of adding * and ? wildcards. This feature is a bit dangerous and performance is somewhat random depending on the position of the wildcard.