deploy: 1c63a120b6

api/basic_json/parser_callback_t.md

@@ -29,7 +29,14 @@ Discarding a value (i.e., returning `#!cpp false`) has different effects dependi
 called:
 
 - Discarded values in structured types are skipped. That is, the parser will behave as if the discarded value was never
-  read.
+  read. This holds for every value type and for both kinds of parent: a discarded element is removed from the
+  surrounding array, and a discarded member is removed from the surrounding object together with its key.
+- Arrays and objects can be discarded either at their `parse_event_t::array_start`/`parse_event_t::object_start` event
+  or at their `parse_event_t::array_end`/`parse_event_t::object_end` event, and both remove the whole value. Discarding
+  it at the start event also means the callback is called neither for the content of the value nor for its matching end
+  event.
+- Discarding a `parse_event_t::key` event discards the whole object member. The callback is still called for the
+  associated value, but its return value has no further effect.
 - In case a value outside a structured type is skipped, it is replaced with `null`. This case happens if the top-level
   element is skipped.
 
@@ -49,7 +56,7 @@ called:
 ## Return value
 
 Whether the JSON value which called the function during parsing should be kept (`#!cpp true`) or not (`#!cpp false`). In
-the latter case, it is either skipped completely or replaced by an empty discarded object.
+the latter case, it is skipped completely, or replaced by `null` if it is the top-level value.
 
 ## Examples
 
@@ -68,6 +75,21 @@ the latter case, it is either skipped completely or replaced by an empty discard
     --8<-- "examples/parse__string__parser_callback_t.output"
     ```
 
+??? example
+
+    The example below shows where discarded values are removed. The array and the number are discarded in different
+    ways, but in each case the parse result contains neither the value nor its key.
+
+    ```cpp
+    --8<-- "examples/parser_callback_t.cpp"
+    ```
+
+    Output:
+
+    ```json
+    --8<-- "examples/parser_callback_t.output"
+    ```
+
 ## See also
 
 - [parse](parse.md) deserialize from a compatible input
@@ -76,3 +98,5 @@ the latter case, it is either skipped completely or replaced by an empty discard
 ## Version history
 
 - Added in version 1.0.0.
+- Fixed in version 3.13.0 to also remove discarded values from a parent object; before, discarding an array or a value
+  stored under an object key left a discarded member behind, which made the parse result serialize to invalid JSON.