YAML: Is it possible to have a list in the root section?

Question

Is it possible to have a list in the root section of an YAML file? So far I've seen no files that follow such a structure and I've been asking myself whether it violates the syntax.

Here is an example:

- 'entry A'
- 'entry B'
- 'entry C'

What I've seen so far:

list:
  - 'entry A'
  - 'entry B'
  - 'entry C'

So in other words, is the list: section obsolete?

Answer 1

It's ok to do that.
Here is a java sample which use snakeYaml:

org.yaml.snakeyaml.Yaml yaml = new org.yaml.snakeyaml.Yaml();
Object o = yaml.load("- 'entry A'\n- 'entry B'\n- 'entry C'");
System.out.println(o.getClass().getName());

The output of the code is :

java.util.ArrayList

But in real scenario, we store an object content into yaml file. When we do that, if the type of one filed is List, we actually store like as you always see:

'field name':
- item1
- item2

Answer 2

No the the scalar list is not obsolete, it defines a completely different structure.

YAML files consist of mappings, sequences and scalars.

• A mapping consists of key-value pairs. A key can be scalars or a list; a value can be a mapping or a sequence or a scalar.
• A list consists of elements and each element can be a mapping, a sequence or a scalar
• A scalar is in principle a string, but certain strings can be interpreted specially ( numbers only -> integers, "False" -> boolean, etc.)

At the top level you can have a (single) scalar (admittedly this is not very flexible):

Hello world

or a mapping:

abc: 
  - 1
  - 2

or a a list:

- 1
- 2  

Your first example has at the top level a sequence consisting of scalars, your second example has at the top level a mapping with a single key-value pair. The key being the scalar list and value being a sequence of scalars.