Why VTT has "Kind:" and "Language:" field? VTT standard doesn't have these

[1c7]

Checklist

• I've looked through the README and FAQ for similar questions
• I'm asking a question
• I've searched the bugtracker for similar questions including closed ones

Run this command

youtube-dl https://www.youtube.com/watch?v=T7Rv4tGRlfc --skip-download --sub-format vtt --write-sub

Get a .vtt file

The Future of Artificial Intelligence - Crash Course AI #20-T7Rv4tGRlfc.en.vtt
Which contain

WEBVTT
Kind: captions
Language: en

00:00:00.240 --> 00:00:05.410
Hey everyone, I’m Jabril and welcome to
the final episode of Crash Course AI.

Question: Why Kind: captions and Language: en exists?

The specification WebVTT: The Web Video Text Tracks Format
doesn't seem like contain Kind: and Language:
It also didn't pass this validator: Live WebVTT Validator

[dstftw]

Ask Youtube why.

[1c7]

OK then, Thanks.

I thought youtube-dl generate these.
(I searched on Github but can't find any code that does this, I just thought maybe I am using the wrong keyword)
but clearly not, Kind: and "Language:" are from Youtube.

Thanks for clarifying