Document the one-character array index change

Add 3.13.0 version-history entries to at, operator[], value, patch,
patch_inplace, and unflatten, and describe in exceptions.md which array
indices throw parse_error.109 and which out_of_range.404.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

docs/mkdocs/docs/api/basic_json/at.md

@@ -241,4 +241,6 @@ Strong exception safety: if an exception occurs, the original value stays intact
 3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
    already supported by [`operator[]`](operator[].md), [`value`](value.md), [`find`](find.md), and other lookup
    functions.
-4. Added in version 2.0.0.
+4. Added in version 2.0.0. Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
+[`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is not
+a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.

docs/mkdocs/docs/api/basic_json/operator[].md

@@ -286,4 +286,6 @@ Strong exception safety: if an exception occurs, the original value stays intact
 3. Added in version 3.11.0. Fixed in version 3.13.0 to consistently accept `std::string_view`-convertible keys, as
    already supported by [`at`](at.md), [`value`](value.md), [`find`](find.md), and other lookup functions.
 4. Added in version 2.0.0. A missing array index in the const version is guarded by a runtime assertion since
-   version 3.13.0.
+   version 3.13.0. Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
+[`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is not
+a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.

docs/mkdocs/docs/api/basic_json/patch.md

@@ -112,3 +112,6 @@ is thrown. In any case, the original value is not changed: the patch is applied
   location has a non-object/non-array parent in version 3.13.0.
 - Added [`out_of_range.414`](../../home/exceptions.md#jsonexceptionout_of_range414) and rejected a "move" operation whose "from" location is a proper
   prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0.
+- Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
+  [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is
+  not a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.

docs/mkdocs/docs/api/basic_json/patch_inplace.md

@@ -110,3 +110,6 @@ function throws an exception.
   location has a non-object/non-array parent in version 3.13.0.
 - Added [`out_of_range.414`](../../home/exceptions.md#jsonexceptionout_of_range414) and rejected a "move" operation whose "from" location is a proper
   prefix of its "path" location instead of silently producing a corrupted result in version 3.13.0.
+- Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
+  [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is
+  not a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.

docs/mkdocs/docs/api/basic_json/unflatten.md

@@ -81,3 +81,6 @@ Apart from these two cases, for a JSON value `j`, the following is always true:
 
 - Added in version 2.0.0.
 - Made the array/object decision independent of the object's iteration order in version 3.13.0.
+- Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109) instead of
+  [`out_of_range.404`](../../home/exceptions.md#jsonexceptionout_of_range404) for a one-character array index that is
+  not a digit (e.g., `/x`) in version 3.13.0, as it already did for longer ones.

docs/mkdocs/docs/api/basic_json/value.md

@@ -227,4 +227,6 @@ changes to any JSON value.
    [`operator[]`](operator[].md), [`at`](at.md), [`find`](find.md), and other lookup functions.
 3. Added in version 2.0.2. Extended to work with arrays in version 3.13.0, including fixing an issue where resolving
    `ptr` through an array unexpectedly threw `out_of_range` instead of returning the resolved element (or
-   `default_value`, as documented).
+   `default_value`, as documented). Throws [`parse_error.109`](../../home/exceptions.md#jsonexceptionparse_error109)
+   instead of returning `default_value` for a one-character array index that is not a digit (e.g., `/x`) in version
+   3.13.0, as it already did for longer ones.

docs/mkdocs/docs/home/exceptions.md

@@ -278,7 +278,9 @@ In a JSON Pointer, only `~0` and `~1` are valid escape sequences.
 
 ### json.exception.parse_error.109
 
-A JSON Pointer array index must be a number.
+A JSON Pointer array index must be a number. This exception is thrown for an array index that does not begin with a
+digit, except for `-` and the empty reference token, which throw [`out_of_range.404`](#jsonexceptionout_of_range404)
+where they cannot be resolved.
 
 !!! failure "Example messages"
 
@@ -289,6 +291,11 @@ A JSON Pointer array index must be a number.
     [json.exception.parse_error.109] parse error: array index '+1' is not a number
     ```
 
+!!! note
+
+    Before version 3.13.0, a one-character array index that is not a digit (e.g., `x`) threw
+    [`out_of_range.404`](#jsonexceptionout_of_range404) instead.
+
 ### json.exception.parse_error.110
 
 When parsing a [binary format](../features/binary_formats/index.md), the byte vector ends before the complete value has
@@ -871,7 +878,8 @@ The provided key was not found in the JSON object.
 
 ### json.exception.out_of_range.404
 
-A reference token in a JSON Pointer could not be resolved.
+A reference token in a JSON Pointer could not be resolved, for instance an array index that begins with a digit but
+contains other characters (e.g., `1a`), or `-` where it cannot be used.
 
 !!! failure "Example message"