Thanks very much :)

This is not exactly a Processing's question you made; but Java's!

Hehe :) Thanks anyway :D

and the reason why replaceAll doesn't work with ^i is that replaceAll() is expecting a regular expression as first argument and '^' has a special meaning in regular expressions (= match at the beginning).

escaping your ^ (using \\) in replaceAll would probably work

replace(), by comparison, takes a string and "^" doesn't mean anything special in strings.

Ah :) Thanks for that, now I understand :)

Why does it take two backslashes to escape the caret?  I tried just one in Processing and got an error, but when I tried it in an online Regex tester, it worked.

Because the regex library wants a (single) backslash, but in Java string, backslash has a special meaning, so it must be escaped. If you want to match a literal backslash, it must be written \\\\
Yes, that's crazy.
Of course, if you input the regular expression in a text field, you can lift the restriction, as long as you double them behind the scene.