Upgrade guide for PHP 5.3: Master namespaces, late static binding, closures, NOWDOC, Phar, and cycles garbage collection while navigating fatal BC breaks like deprecated ereg and call-time pass-by-reference removal.

PHP 5.4 upgrade guide: Learn traits, short array syntax, callable type hints, automatic $this in closures, and how to migrate legacy code after the removal of magic quotes and register_globals.

PHP 5.5 upgrade guide: Learn memory-efficient generators (yield), try-catch finally blocks, the native password hashing API, ClassName::class syntax, and how to migrate away from deprecated mysql and preg_replace /e.

PHP 5.6 upgrade guide: Learn variadic parameters, argument unpacking with ..., the exponentiation operator **, use function/const namespace imports, constant expressions, hash_equals, and strict SSL/TLS defaults.

PHP 7.0 upgrade guide: scalar type declarations, return types, null coalescing (??), spaceship operator (<=>), anonymous classes, Throwable, CSPRNG, and major BC breaks.

PHP 7.1 upgrade guide: nullable types, void returns, class constant visibility, symmetric array destructuring, iterable pseudo-type, multi-catch, negative string offsets, and BC breaks.

PHP 7.2 upgrade guide: object type hint, parameter type widening, PDO debug dumps, LDAP EXOP, addrinfo sockets API, libsodium—plus BC (count, get_class, object/array casts) and mcrypt removed to PECL.

PHP 7.3 upgrade guide: flexible heredoc/nowdoc, trailing commas in calls, reference destructuring, is_countable, array_key_first/last, JsonException, Argon2id, PCRE2—and BC breaks that affect real code.

PHP 7.4 upgrade guide: typed properties, arrow functions, variance, ??=, spread in arrays, WeakReference, __serialize/__unserialize, OPcache preloading, FFI—and the BC breaks that hit real apps.

Explore PHP 8.0 after 7.4: named arguments, match, nullsafe, attributes, JIT, union types—what breaks, what to rewrite, and runnable examples.

PHP 8.1 after 8.0: enums, readonly properties, fibers, intersection/never types, first-class callables—plus $GLOBALS rules, MySQLi exceptions, and a deprecation watchlist.

PHP 8.2 guide: readonly classes, standalone null/false/true types, DNF types, #[SensitiveParameter], Random extension, dynamic property deprecations, and BC breaks from 8.1.