This search engine supports Perl Regular Expressions (regexes)

For example, . will match any character (eg: s.t matches sat, sit, etc.).
+ will match one or more of the previous character (eg: blu+e will match blue, bluue, etc.)
[a-z] will match any Latin lowercase letter
[e-i] will match any of e, f, g, h, or i

For more on regexes, see this tutorial.