Depending on your permissions, here you can specify or just view the unique PHP configuration for this website (apart from the other sites in your subscription). Custom PHP configuration might be useful when you want to limit the system resources consumption by PHP scripts or meet the requirements of a certain web app. When you set a parameter to Default value, PHP will use the parameter's value from the server-wide PHP configuration.
You can use the following placeholders in parameter values:
{DOCROOT} for the document root directory of this website.
{WEBSPACEROOT} for the document root directory of a webspace which holds this website.
{TMP} for the directory which stores temporary files.