Method 1 & 2 & 3
https:///...-standards-error-fix
Method 4
error_reporting(0);
ini_set('display_errors', '0'); # don't show any errors...
error_reporting(E_ALL | ~E_STRICT); # ...but do log them
Few more
http:///...-standards-in-joomla
https:///...-reporting-explained
