Windows 7
SlickEdit Pro 2018 (v23.0.0.11 64-bit)
Config\23.0.0\hotfixes\hotfix_se2300_1_cumulative.zip (Revision: 1)
Pressing '?' to do a backwards search and adding the /i does not work.
For example: ?some_string/i
Forward search with '/' does work.
For example /some_string/i
Also, vim with vim syntax backward search works:
?some_string\c
I haven't tried other switches.