Custom converters

Subclass Avm1Converter<T> to own the read/write of a type:

public sealed class CoordConverter : Avm1Converter<Coord>
{
    public override Coord Read(Avm1Value v, Avm1SerializerOptions o)
    {
        var parts = v.AsString.Split(',');
        return new Coord(int.Parse(parts[0]), int.Parse(parts[1]));
    }

    public override Avm1Value Write(Coord c, Avm1SerializerOptions o) => new Avm1String($"{c.X},{c.Y}");
}

Attach it to a type or a member, or register it on the options.

Resolution order

Resolution order (highest first):

1. [Avm1Converter] on the member.
2. a converter in Options.Converters (first whose CanConvert matches; Avm1ConverterFactory instances are asked to create one).
3. [Avm1Converter] on the type.
4. the built-in converter.

A type handled by a custom converter is opaque: it has no configurable properties and is read/written wholly by the converter — the same rule System.Text.Json uses.