php/php-src — pull request #437 by strysd (2013-09-11 03:55:31+00:00)
Title: changes default value of mbstring.substitute_character

Current default value of mbstring.substitute_character seems to be unavailable, so I think it should be changed from none to NULL , 63 (0x3F), or "none" .
I believe the 63 has clear difinition and backward compatibility .