This function returns a copy of str, translating all occurrences of each character in from to the corresponding character in to.
If from and to are different lengths, the extra characters in the longer of the two are ignored.
strtr() may be called with only two arguments. If called with two arguments it behaves in a new way: from then has to be an array that contains string -> string pairs that will be replaced in the source string. strtr() will always look for the longest possible match first and will *NOT* try to replace stuff that it has already worked on.
Nota: This optional to and from parameters were added in PHP 4.0.0
See also ereg_replace().