0.02 0.02 >$,='|'

|0.02|0.02|>$s = qq(the quick brown fox jumps over the lazy dog)

# Used this way, the return is the 4 bytes replaced.
|0.02|0.02|>print substr($s,0,4,''),$s
the |quick brown fox jumps over the lazy dog

|0.02|0.02|>print $s
quick brown fox jumps over the lazy dog

# But used this way, it is the first 4 bytes *after* the replacement occurs?
|0.02|0.02|>print substr($s,0,4)='',$s
k br|k brown fox jumps over the lazy dog

|0.02|0.02|>print $s
k brown fox jumps over the lazy dog