Leetspeak Translator

Write text in leetspeak at one of three intensities, or read leetspeak back into plain text. Basic swaps the six canonical letters (a4 e3 i1 o0 s5 t7), advanced adds four more, and extreme builds most of the alphabet out of punctuation. Decoding is best effort because leet is ambiguous: the digit 1 stands for both i and l, and this resolves it to l.