In the header object of an HTTP header, can there be only regulated properties?

Question

Computer networks

In the code I'm parsing, this is the construction of the http request header:

headers: {
                'Content-Type': 'application/json',
                'x-access-token': token
            }

The x-access-token property is not in the lists of http headers I found on various sites. Or can I pass whatever properties I want in the header?

Answer 1

headers starting with X are custom.
https://en.wikipedia.org/wiki/List_of_HTTP_header_...