Psych::Nodes::Scalar::LITERAL ignored in encode_with?

[akunszt]

This could just me, but I really lost and I don't understand why this works this way.

I have a big YAML with various string values. One of them is an encoded file content which is nice for machine consumption but I want to show that as a literal for human beings.

I created a separate class for those values and I added an encode_with method.

 def encode_with( coder )
 coder.scalar = @str 
 coder.tag = "!file_content"
 coder.style = Psych::Nodes::Scalar::LITERAL
 end

When the value is short then it works as expected but if it is longer then output is still quoted.

---
hello: world
short: !file_content |
 TEST_DOCKER_IMAGE="foobar/image:1.2.3-r4"
long: !file_content "!\n! %[CONN_NAME]\n!\nneighbor %[REMOTE_ADDRESS] remote-as %[REMOTE_ASN]\nneighbor
 %[REMOTE_ADDRESS] description %[CONN_NAME]\naddress-family ipv6\n\tneighbor %[REMOTE_ADDRESS]
 activate\n\tneighbor %[REMOTE_ADDRESS] soft-reconfiguration inbound\n\tneighbor
 %[REMOTE_ADDRESS] prefix-list ipv6_ranges in\n\tneighbor %[REMOTE_ADDRESS] prefix-list
 ipv6_ranges out\n\tneighbor %[REMOTE_ADDRESS] route-map add_extra_hop in\n\tneighbor
 %[REMOTE_ADDRESS] route-map no_advertise_self out\nexit-address-family\n"

The documentation is quite scarce about this topic. Do I miss something? Or is this a bug in Psych?