Wiki

YAML is a simple human-readable format. It is simpler than XML or JSON, yet still very expressive.
We will need only a small number of elements of the syntax to define our applications.

1: --- starts a new section (in our case -- an application)

2: key: value pairs define keys and their values. The value can be a multi-word string (quoting is optional)

#!YAML

key1 : value1
key2 : "value for key 2"
key3 : value\with\backslashes
key4 : "value\\with\\escaped\\backslashes"

Note: On Windows systems backslash is used to separate directories in a path.
Within double-quotes the backslashes ought to be escaped (like in key4)

3: key: | starts a multi-line value string. It has to be indented.

#!YAML

multiString : |
    She sells
    sea-shells
    at sea shore.

Further info:

Wiki on YAML

Online validator (one of many)