ArduinoJson 6.21.0
* Drop support for C++98/C++03. Minimum required is C++11.
* Remove `ARDUINOJSON_NAMESPACE`; use `ArduinoJson` instead.
* Make string support generic (issue #1807)

ArduinoJson 6.20.1
* Remove explicit exclusion of `as<char*>()` and `as<char>()` (issue #1860)

ArduinoJson 6.20.0
* Add `JsonVariant::shallowCopy()` (issue #1343)
* Fix `9.22337e+18 is outside the range of representable values of type 'long'`
* Fix comparison operators for `JsonArray`, `JsonArrayConst`, `JsonObject`, and `JsonObjectConst`
* Fix lax parsing of `true`, `false`, and `null` (issue #1781)
* Remove undocumented `accept()` functions
* Rename `addElement()` to `add()`
* Remove `getElement()`, `getOrAddElement()`, `getMember()`, and `getOrAddMember()`
* Remove undocumented `JsonDocument::data()` and `JsonDocument::memoryPool()`
* Remove undocumented `JsonArrayIterator::internal()` and `JsonObjectIterator::internal()`
* Rename things in `ARDUINOJSON_NAMESPACE` to match the public names
* Add documentation to most public symbols
* Remove support for naked `char` (was deprecated since 6.18.0)

ArduinoJson 6.19.4
* Add `ElementProxy::memoryUsage()`
* Add `MemberProxy::memoryUsage()` (issue #1730)
* Add implicit conversion from `JsonDocument` to `JsonVariant`
* Fix comparisons operators with `const JsonDocument&`

ArduinoJson 6.19.3
* Fix `call of overloaded 'String(const char*, int)' is ambiguous`
* Fix `JsonString` operator `==` and `!=` for non-zero-terminated string
* Fix `-Wsign-conversion` on GCC 8 (issue #1715)
* MessagePack: serialize round floats as integers (issue #1718)

ArduinoJson 6.19.2
* Fix `cannot convert 'pgm_p' to 'const void*'` (issue #1707)

ArduinoJson 6.19.1
* Fix crash when adding an object member in a too small `JsonDocument`
* Fix filter not working in zero-copy mode (issue #1697)

ArduinoJson 6.19.0
* Remove `ARDUINOJSON_EMBEDDED_MODE` and assume we run on an embedded platform.

ArduinoJson 6.18.5
* Set `ARDUINOJSON_EMBEDDED_MODE` to `1` on Nios II (issue #1657)

ArduinoJson 6.18.4
* Fixed error `'dummy' may be used uninitialized` on GCC 11
* Fixed error `expected unqualified-id before 'const'` on GCC 11 (issue #1622)
* Filter: exact match takes precedence over wildcard (issue #1628)
* Fixed deserialization of `\u0000` (issue #1646)

ArduinoJson 6.18.3
* Changed return type of `convertToJson()` and `Converter<T>::toJson()` to `void`
* Added `as<std::string_view>()` and `is<std::string_view>()`

ArduinoJson 6.18.2
* Removed a symlink because the Arduino Library Specification forbids it

ArduinoJson 6.18.1
* Fixed support for `volatile float` and `volatile double` (issue #1557)
* Fixed error `[Pe070]: incomplete type is not allowed` on IAR (issue #1560)
* Fixed `serializeJson(doc, String)` when allocation fails (issue #1572)
* Fixed clang-tidy warnings (issue #1574, PR #1577 by @armandas)
* Added fake class `InvalidConversion<T1,T2>` to easily identify invalid conversions (issue #1585)
* Added support for `std::string_view` (issue #1578, PR #1554 by @0xFEEDC0DE64)
* Fixed warning `definition of implicit copy constructor for 'MsgPackDeserializer' is deprecated because it has a user-declared copy assignment operator`
* Added `JsonArray::clear()` (issue #1597)
* Fixed `JsonVariant::as<unsigned>()` (issue #1601)
* Added support for ESP-IDF component build (PR #1562 by @qt1, PR #1599 by @andreaskuster)

ArduinoJson 6.18.0
* Added support for custom converters (issue #687)
* Added support for `Printable` (issue #1444)
* Removed support for `char` values, see below (issue #1498)
* `deserializeJson()` leaves `\uXXXX` unchanged instead of returning `NotSupported`
* `deserializeMsgPack()` inserts `null` instead of returning `NotSupported`
* Removed `DeserializationError::NotSupported`
* Added `JsonVariant::is<JsonArrayConst/JsonObjectConst>()` (issue #1412)
* Added `JsonVariant::is<JsonVariant/JsonVariantConst>()` (issue #1412)
* Changed `JsonVariantConst::is<JsonArray/JsonObject>()` to return `false` (issue #1412)
* Simplified `JsonVariant::as<T>()` to always return `T` (see below)
* Updated folders list in `.mbedignore` (PR #1515 by @AGlass0fMilk)
* Fixed member-call-on-null-pointer in `getMember()` when array is empty
* `serializeMsgPack(doc, buffer, size)` doesn't add null-terminator anymore (issue #1545)
* `serializeJson(doc, buffer, size)` adds null-terminator only if there is enough room
* PlatformIO: set `build.libArchive` to `false` (PR #1550 by @askreet)

ArduinoJson 6.17.3
* Made `JsonDocument`'s destructor protected (issue #1480)
* Added missing calls to `client.stop()` in `JsonHttpClient.ino` (issue #1485)
* Fixed error `expected ')' before 'char'` when `isdigit()` is a macro (issue #1487)
* Fixed error `definition of implicit copy constructor is deprecated` on Clang 10
* PlatformIO: set framework compatibility to `*` (PR #1490 by @maxgerhardt)

ArduinoJson 6.17.2
* Fixed invalid conversion error in `operator|(JsonVariant, char*)` (issue #1432)
* Changed the default value of `ARDUINOJSON_ENABLE_PROGMEM` (issue #1433).

ArduinoJson 6.17.1
* Fixed error `ambiguous overload for 'operator|'` (issue #1411)
* Fixed `operator|(MemberProxy, JsonObject)` (issue #1415)
* Allowed more than 32767 values in non-embedded mode (issue #1414)

ArduinoJson 6.17.0
* Added a build failure when nullptr is defined as a macro (issue #1355)
* Added `JsonDocument::overflowed()` which tells if the memory pool was too small (issue #1358)
* Added `DeserializationError::EmptyInput` which tells if the input was empty
* Added `DeserializationError::f_str()` which returns a `const __FlashStringHelper*` (issue #846)
* Added `operator|(JsonVariantConst, JsonVariantConst)`
* Added filtering for MessagePack (issue #1298, PR #1394 by Luca Passarella)
* Moved float convertion tables to PROGMEM
* Fixed `JsonVariant::set((char*)0)` which returned false instead of true (issue #1368)
* Fixed error `No such file or directory #include <WString.h>` (issue #1381)

ArduinoJson 6.16.1
* Fixed `deserializeJson()` that stopped reading after `{}` (issue #1335)

ArduinoJson 6.16.0
* Added comparisons (`>`, `>=`, `==`, `!=`, `<`, and `<=`) between `JsonVariant`s
* Added string deduplication (issue #1303)
* Added `JsonString::operator!=`
* Set `ARDUINOJSON_DECODE_UNICODE` to `1` by default
* Fixed `copyArray()` not working with `String`, `ElementProxy`, and `MemberProxy`
* Fixed error `getOrAddElement is not a member of ElementProxy` (issue #1311)
* Fixed excessive stack usage when compiled with `-Og` (issues #1210 and #1314)
* Fixed `Warning[Pa093]: implicit conversion from floating point to integer` on IAR compiler (PR #1328 by @stawiski)