The RFC proposes to deprecate the listed functionality in PHP 8.4 and remove it in PHP 9 (except where otherwise noted).
Formally deprecate and remove the aforementioned DOMDocument and DOMEntity properties?
Remove DOMImplementation::getFeature($feature, $version)
Deprecate DOM_PHP_ERR constant?
Deprecate unserialize()’s ‘S’ tag?
Deprecate the INI settings ‘session.sid_length’ and ‘session.sid_bits_per_character’?
Deprecate SplFixedArray::__wakeup()?
Deprecate xml_set_object() and xml_set_*_handler() with string method names
Deprecate passing null and false to dba_key_split()
Deprecate passing incorrect data types for options to ext/hash functions
Deprecate constants SUNFUNCS_RET_STRING, SUNFUNCS_RET_DOUBLE, and SUNFUNCS_RET_TIMESTAMP?
Deprecate passing a non-empty string to the $escape parameter
Remove the E_STRICT Error Level and Deprecate the E_STRICT constant?
Deprecate returning non-string values from a user output buffer handler?
Deprecate producing output in a user output handler?
Deprecate using an array as the $data argument for file_put_contents()
Deprecate mysqli_ping() and mysqli::ping()?
Deprecate mysqli_refresh(), mysqli::refresh() and related constants?
Deprecate mysqli_kill() and mysqli::kill()?
Deprecate the second parameter to mysqli_store_result()?
Deprecate md5(), sha1(), md5_file(), and sha1_file()?
Deprecate passing E_USER_ERROR to trigger_error()
Deprecate using a single underscore as a class name?
Deprecate SOAP_FUNCTIONS_ALL constant and passing it to SoapServer::addFunction()?