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yaml as file extension. Different documents in YAML can be separated using three dashes ( --- ). You use three dots ( ... ) to mark the end of a document without starting a new one. A document in block style uses spaces to structure the document. Flow style makes YAML an extension of JSON .
All YAML files (regardless of their association with Ansible or not) can optionally begin with --- and end with ... . This is part of the YAML format and indicates the start and end of a document. All members of a list are lines beginning at the same indentation level starting with a "- " (a dash and a space):
In general the order of keys in a YAML file does not matter. Neither do blank lines. Indentation may be with any number of spaces, as long as it is consistent throughout the file.
YAML always requires colons and commas used as list separators followed by space with scalar values. Nodes should be labelled with an exclamation mark (!) or double exclamation mark (!!), followed by string which can be expanded into an URI or URL.
As you already found out, the three dashes --- are used to signal the start of a document, i.e.:
To signal the document start after directives, i.e., %YAML or %TAG lines according to the current spec. For example:
%YAML 1.2
%TAG !foo! !foo-types/
---
myKey: myValue
To signal the document start when you have multiple yaml documents in the same stream, e.g., a yaml file:
doc 1
---
doc 2
If doc 2 has some preceding directives, then we have to use three dots ... to indicate the end of doc 1 (and the start of potential directives preceding doc 2) to the parser. For example:
doc 1
...
%TAG !bar! !bar-types/
---
doc 2
The spec is good for yaml parser implementers. However, I find this article easier to read from a user perspective.
It's not mandatory to have them if you do not begin your YAML with a directive. If it's the case, you should use them.
Let's take a look at the documentation
3.2.3.4. Directives
Each document may be associated with a set of directives. A directive has a name and an optional sequence of parameters. Directives are instructions to the YAML processor, and like all other presentation details are not reflected in the YAML serialization tree or representation graph. This version of YAML defines a two directives, “YAML” and “TAG”. All other directives are reserved for future versions of YAML.
One example of this can also be found in the documentation for directive YAML
%YAML 1.2 # Attempt parsing
# with a warning
---
"foo"
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