Derives the [`SerializationGroup`] trait for a type.
To configure the serialization, use the `#[xgroup(...)]` attribute on the root of the type.
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<strong>NOTE:</strong> This trait/attribute is not mutually exclusive with the [Serialize] trait/attributes. This means that you could for example use a struct both as a sequence ([Serialize] with no attribute) and as a group ([SerializationGroup] with the attribute). This does naturally however require no attribute on the root of the type, or the attributes themselves need to implement [Serialize] as well.
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[Serialize]: Serialize
[SerializationGroup]: SerializationGroup
## Configuration
### Serialize a part of an element - `#[xgroup(...)]` on the root of a type
#### Root Options
None for serialization currently.