Take it apart.

You start with .* which can match an empty string.

Then you have (?i) which is a directive and does not match anything.

Then you have d? which can match an empty string.

Then you have max which must match the sequence "m", "a", and "x" but could be upper or lower case.

Then you have another .* which can also match an empty string.

It looks to me like you've built a complicated string to search for occurrences of "max". What were you trying to do?