A Question was asked on the wp-hackers mailing list:
Does a map of PHP versions to available functions exist? I can look up the
PHP function reference to see which version a function appeared in, but I’m
not aware of a reverse mapping (and I must be Googling very badly today).
Well.. I couldnt find one either, So i created a hacked-together list very quickly: http://dd32.id.au/php-functions-by-version.htm
It simply allows you to view what functions were added to a specific PHP version, This was prompted by WordPress moving to PHP 4.3+ for version 2.5 which is due out later this year.
Hopefully its of use to someone.