Using stringreplace without changing case

[cayci dmer]

Hi,
I want to make a case-insesitive replace, while preserving the case.
For example, let stringreplacexxx be the function that does what I
want:

ostr:='The quick brown fox jumped over another FoX';
tc:='fox';
nstr:=stringreplacexxx(ostr,tc,'<b>'+tc+'</b>');

So at last ostr will be; 'The quick brown <a>fox</a> jumped over
another <a>FoX</a>'

I could not achieve this with stringreplace, it gives me; 'The quick
brown <a>fox</a> jumped over another <a>fox</a>'. Is there smart way to
accomplish this?