YAML Inline Extend syntax cannot be parsed

[Vampire]

The blog post https://blog.daemonl.com/2016/02/yaml.html shows that there is an "inline extend" syntax where this YAML

foo:
 <<: &anchor
   K1: "One"
 K2: "Two"

bar:
 <<: *anchor
 K3: "Three"

defines this JSON

{
    "foo": {
        "K1": "One",
        "K2": "Two"
    }, 
    "bar": {
        "K1": "One",
        "K3": "Three"
    }
}

But If I give the mentioned YAML to prettier, I am greeted with this error:

[error] test.yml: SyntaxError: Merge nodes can only have Alias nodes as values (2:2)
[error]   1 | foo:
[error] > 2 |  <<: &anchor
[error]     |  ^^^^^^^^^^^
[error] > 3 |    K1: "One"
[error]     | ^^^^^^^^^^^^
[error] > 4 |  K2: "Two"
[error]     | ^^^^^^^^^^^^
[error] > 5 | 
[error]     | ^
[error]   6 | bar:
[error]   7 |  <<: *anchor
[error]   8 |  K3: "Three"

Sending given YAML through js-yaml produces the exact expected result.
It would be nice if prettier would support this syntax too.

[alexander-akait]

We should improve it on parser side firstly prettier/yaml-unist-parser#273

[alexander-akait]

Can be implemented prettier/yaml-unist-parser#273, PR welcome