regex or query function on filter criterion

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Hi, we have used $co operator on a field filter criterion on our SDP for table data search. Our search results for LIKE, EXACT work fine.

Any symbols/wild card characters such as *, ?, and % are fetching entire result set but other symbols $, # and etc return 'no data'.  

1>  I want search to result with *searchText, *searchText*, searchText* and not entire data set? how to we achieve this?

2> Please guide how to provide regex parameters too? I have tried providing [A-Z, a-z,0-9, *%?_] within value of regex operator but it doesn't work/ not right.

3> can we club 2 operators in filter criterion? $co and $regex?