Описание тега php-shorttags
PHP short open tag which was disabled by default ini configuration since PHP 5.3.0.
Also known as the short_open_tag PHP ini setting.
Disabled by default ini suggestions since PHP 5.3.0. See tags not working in php 5.3.1.
Since PHP 5.3.0, the setting directive of the first notation is not PHP_INI_ALL anymore but PHP_INI_PERDIR.
Since PHP 5.4.0 the directive is not controlling the shorthand <?= any longer.