What maps

A member maps when its type is one of:

• Scalars — string, bool, every numeric type (byte/sbyte/short/ushort/int/uint/long/ulong/float/double/decimal), and enum (written as its numeric value). All numbers are widened to double in the AVM1 tree.
• Nested objects — any other class/record/struct. Its members are bound the same way; no marker attribute is needed.
• Collections — T[], List<T> (or IList<T>/IReadOnlyList<T>/IEnumerable<T>), and Dictionary<string, V> (or IDictionary/IReadOnlyDictionary). Elements and values may be any supported type, so int[][] and Dictionary<string, Dictionary<string, int[]>> nest freely.
• Pass-through — Avm1Value, Avm1Object, Avm1Array: stored and restored verbatim, the escape hatch for irreducibly heterogeneous data.
• Custom — anything, via [Avm1Converter] (see Converters).

Only public and internal members participate; static, const, and [Avm1Ignore] members are skipped.

Construction

On read the serializer builds the instance one of two ways:

• Constructor binding — a positional record, or a type with a single parameterized constructor: each parameter is matched to a member by name (case-insensitive) and supplied from the tree.
• Object initializer — a type with an accessible parameterless constructor (or a struct): the instance is created, then each settable member (set or init) is assigned.

public record Job(int Group, string Name);                 // constructor binding

public class Settings { public string? Theme { get; init; } public bool Mute { get; init; } }

If a type has several constructors and the choice is ambiguous, mark one with [Avm1Constructor]:

public class Box
{
    public Box(int a) { ... }
    [Avm1Constructor] public Box(int a, int b) { ... }   // this one is used
}

A type with no usable constructor reports AVM1003.

Optional members, null, and defaults

A nullable member (int?, string?, Weapon?, List<int>?, …) is optional: a null value is omitted on write, and a missing key reads back as null.

A non-nullable reference / nested / pass-through member is required-on-read — a missing key throws (a runtime Avm1SerializationException). A non-nullable numeric/bool/enum silently defaults to 0/false on a missing key unless you add [Avm1Required]. Collections default to empty.

Write behaviour for null is controlled by Avm1SerializerOptions.DefaultIgnoreCondition — see Options.