short_open_tag is a bit of an 'old school' PHP setting, and was used a lot in PHP versions up to and including PHP 5.6. It is a is a deprecated feature of PHP now and it is highly recommended to use the full tag combination instead (i.e. <?php and ?>). The directive is still available for you to use for backwards compatibility. Errors like the below would indicate that short tags are in use:
PHP message: PHP Parse error: syntax error, unexpected end of file, expecting else if (T_ELSEIF) or else (T_ELSE) or endif (T_ENDIF)
You can turn short_open_tags on in the Platform in the PHP Configuration section of a website. Log in to the Platform, select the website from the dashboard and then from the website dashboard either select Upgrade PHP version or PHP & Databases from the side panel.
Scroll down to the PHP Configuration section, click Add Variable and if you start typing short_open_tag in the first box on the new line you'll see the option to select it. The correct value for this setting is On. Click Update Configuration to saving the change.