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.

PHP 8.3 from 8.2: #[Override], typed class constants, readonly clone tweaks, json_validate, str_increment/str_decrement, safer range() and proc_get_status(), assert INI deprecation, and migration pitfalls.

PHP 8.4 upgrade notes (from 8.3): Property Hooks, asymmetric visibility, Lazy Objects, #[Deprecated], request_parse_body(), new Dom\* API, new array_* helpers, and the most important BC breaks & deprecations.

PHP 8.5 from 8.4: |> pipe operator, #[NoDiscard] and (void), closures in constant expressions, ext/uri, FILTER_THROW_ON_FAILURE, Opcache in binary, PDO fetch constant changes, and deprecations to plan for.