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Extension data captures unknown keys during deserialization.

This is useful for:

• forward-compatible configuration formats
• preserving unrecognized settings when a model is partial

Dictionary-based extension data

using SharpYaml.Serialization;

public sealed class Config
{
    public int Known { get; set; }

    [YamlExtensionData]
    public Dictionary<string, object?>? Extra { get; set; }
}

If the extension data property is , SharpYaml will create a new dictionary instance when unknown keys are encountered. If no unknown keys are encountered, the property is left as .

Mapping-based extension data

If you need a YAML-native representation (for example to preserve YAML shapes), use SharpYaml.Model.YamlMapping:

using SharpYaml.Model;
using SharpYaml.Serialization;

public sealed class Config
{
    [YamlExtensionData]
    public YamlMapping? Extra { get; set; }
}