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Mention the YAML features not supported by the Yaml component #8249

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Mention the YAML features not supported by the Yaml component
javiereguiluz Aug 1, 2017
2da64a7
Fixes
javiereguiluz Sep 6, 2017
4c47276
Fixed a syntax issue
javiereguiluz Sep 7, 2017
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37 changes: 24 additions & 13 deletions components/yaml/yaml_format.rst
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Expand Up @@ -4,16 +4,11 @@
The YAML Format
===============

According to the official `YAML`_ website, YAML is "a human friendly data
serialization standard for all programming languages".

Even if the YAML format can describe complex nested data structure, this
article only describes the minimum set of features needed to use YAML as a
configuration file format.

YAML is a simple language that describes data. As PHP, it has a syntax for
simple types like strings, booleans, floats, or integers. But unlike PHP, it
makes a difference between arrays (sequences) and hashes (mappings).
According to the official `YAML website`_, YAML is "a human friendly data
serialization standard for all programming languages". The Symfony Yaml
component implements a subset of the `YAML specification`_. Specifically, it
implements the minimum set of features needed to use YAML as a configuration
file format.

Scalars
-------
Expand Down Expand Up @@ -171,8 +166,8 @@ Collections
-----------

A YAML file is rarely used to describe a simple scalar. Most of the time, it
describes a collection. A collection can be a sequence or a mapping of
elements. Both sequences and mappings are converted to PHP arrays.
describes a collection. YAML collections can be a sequence (indexed arrays in PHP)
or a mapping of elements (associative arrays in PHP).

Sequences use a dash followed by a space:

Expand Down Expand Up @@ -318,4 +313,20 @@ The YAML specification defines some tags to set the type of any data explicitly:
Pz7Y6OjuDg4J+fn5OTk6enp
56enmleECcgggoBADs=

.. _YAML: http://yaml.org/
Unsupported YAML Features
-------------------------

The following YAML features are not supported by the Symfony Yaml component:

* Multi-documents (``---`` and ``...`` markers);
* Complex mapping keys and complex values starting with ``?``;
* Tagged values as keys;
* The following tags and types: `!!set`, `!!omap`, `!!pairs`, `!!set`, `!!seq`,
`!!bool`, `!!int`, `!!merge`, `!!null`, `!!timestamp`, `!!value`, `!!yaml`;
* Tags (``TAG`` directive; example: ``%TAG ! tag:example.com,2000:app/``)
and tag references (example: ``!<tag:example.com,2000:app/foo>``);
* Using sequence-like syntax for mapping elements (example: ``{foo, bar}``; use
``{foo: ~, bar: ~}`` instead).

.. _`YAML website`: http://yaml.org/
.. _`YAML specification`: http://www.yaml.org/spec/1.2/spec.html