The context options

Five keys of the serialization context change how a document is written. Each one is the context form of a flag of Encoder.

// A float on four bytes rather than eight
$cbor = $serializer->serialize($data, 'cbor', [
    'cbor_single_precision_float' => true,
]);

// Arrays in their indefinite-length form
$cbor = $serializer->serialize([1, 2, 3], 'cbor', [
    'cbor_indefinite_list' => true,
]);

// Maps in their indefinite-length form
$cbor = $serializer->serialize(['a' => 1], 'cbor', [
    'cbor_indefinite_map' => true,
]);

// Text strings in their indefinite-length form
$cbor = $serializer->serialize('Hello', 'cbor', [
    'cbor_indefinite_text_string' => true,
]);

Key	What it does
cbor_single_precision_float	writes a float on 32 bits instead of 64
cbor_indefinite_text_string	writes text strings in their indefinite-length form
cbor_indefinite_byte_string	the same, for byte strings
cbor_indefinite_list	the same, for arrays
cbor_indefinite_map	the same, for maps

All five take a boolean and default to false. They can be combined, and each one applies to the whole document rather than to one item of it.

Single precision loses digits

cbor_single_precision_float halves the room a float takes, and keeps about seven significant decimal digits instead of sixteen. It is the right choice for a sensor reading and the wrong one for an amount of money — for which neither float is right: use a decimal fraction.