Copyright © 2001-2005 Oren Ben-Kiki, Clark Evans, Brian Ingerson
Status
This specification is a draft reflecting consensus reached by members of the yaml-core mailing list. Any questions regarding this draft should be raised on this list.
URI:
tag:yaml.org,2002:yaml
Shorthand:
!!yaml
Kind:
Scalar.
Canonical:
N/A (single format).
Regexp:
!|&|\*
Definition:
Keys for encoding YAML in YAML.
YAML encoding keys are used to denote YAML structure information. The in-memory representation of these keys must be different from any value in any other type family. Specifically, these in-memory values must not be implemented as strings. Normally, the encoding keys should not be used in serialized YAML documents; the encoded YAML node is serialized instead.
Encoding is useful when a YAML processor encounters a valid YAML value of an unknown tag. For a schema-specific application, this is not different from encountering any other valid YAML document that does not satisfy the schema. Such an application may safely use a processor that rejects any value of any unknown tag, or discards the tag property with an appropriate warning and parses the value as if the property was not present.
For a schema-independent application (for example, a hypothetical
YAML pretty print application), this is not an option. Processors
used by such applications should encode the value instead. This may
be done by wrapping the value in a mapping containing encoding
keys. The “!” key denotes the
unsupported tag. In some cases it may be necessary to encode
anchors and alias nodes as well. The
“&” and
“*” keys are used for this
purpose.
Encoding should be reversed on output, allowing the schema-independent application to safely round-trip any valid YAML document. In-memory, the encoded data may be accessed and manipulated in a standard way using the three basic data types (mapping, sequence and scalar), allowing limited processing to be applied to arbitrary YAML data.