When min_infix_len is enabled, you can use following special characters in words:
? match one letter
% match zero or one letter
* match zero or more letters
(I don’t remember where exactly this is documented, this was a bit difficult to find as this is NOT mentioned in “Extended query syntax” as one might expect.)
Tried with min_prefix_len = 1 and min_word_len = 1, got more results (85 out of mysql’s 102), even so it doesn’t match words like lil_johndoe_24mr_johndoe23 or johndoe_i_am