What does extra mean in VK api?

Question

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Question for self-development
What does the extra parameter mean in VK api?
Examples:
Earlier in the VC audio return parameter url: http:? \ / \ / Cs9-11v4.vk.me \ / p13 \ /39a25fcb2c8ce0.mp3 extra = hLsHqDEzrwLWudHCpV1RRIAEHmwymoX6DyWikmJFCpjhdS_xrATqtAtC9trWSyyd1asFakko8BvXCTkjfQKEPlqdVFL6And
now here's a link to a picture of the comment:
https: // cs7056 .userapi.com/c812736/u48044422/docs/...
Although if you do not use this parameter, it also opens normally.
In general, what could it be for?

Answer 1

Binding to ip, all that.

Answer 2

Yes, binding to API or user id