@Override
        public void apply(Shape shape, Node value, Context context, Emitter emitter) {
            if (isTimestampMember(context.model(), shape) && !value.isNumberNode()) {
                emitter.accept(shape,
                        "Invalid " + value.getType() + " value provided for timestamp, `"
                                + shape.getId() + "`. Expected a number that contains epoch "
                                + "seconds with optional millisecond precision");
            }
        }
Requires that the value provided for all timestamp shapes is a
unix timestamp.
smithy-model/src/main/java/software/amazon/smithy/model/validation/node/TimestampValidationStrategy.java