pattern is specified sub string which will be replace (case sensitive).
replacement is other sub string which will replace the pattern.
1. The result of script below are same with original string object, because the string object doesn't contain sub string pattern.
The pattern is "Split" and string object doesn't contain this pattern, so the result is "String Manipulation Using split() Method".
2. The result of script bellow replace the original string object.The pattern is "split" and string object contain this pattern, so the result is "Manipulation Using replace() Method".