Anonymous Monk,
I provided 3 examples because you were not exactly clear what your definition of "case insensitive" and "case sensitive" was in your post. The second example is closest to what you mean, but you might have also meant:

$string =~ s/(jane)/##$1##/i;
[download]

This would allow any letters to be any case, but be preserved in the replacement.

Cheers - L~R