john without a capital J
John with a capital J
JOHN in Upper case

Code for overloading the :contains selector to be case insensitive:

 
            jQuery.expr[':'].Contains = function(a, i, m) {
              return jQuery(a).text().toUpperCase()
                  .indexOf(m[3].toUpperCase()) >= 0;
            };
            jQuery.expr[':'].contains = function(a, i, m) {
              return jQuery(a).text().toUpperCase()
                  .indexOf(m[3].toUpperCase()) >= 0;
            };

Without the overload on the :contains selector jquery would normaly only underline the second line