On Thu, 28 Jan 2016 09:06:01 -0500, Stormin Mormon
wrote:

How do you describe it when you post text in
the center of an existing post?

Micky explained it to you. The same as intended. it isn't "center"
posting. It is "in-line" posting, to reply to a specific comment.

"...An RFC is authored by engineers and computer scientists in the
form of a memorandum describing methods, behaviors, research, or
innovations applicable to the working of the Internet and
Internet-connected systems. "

https://en.wikipedia.org/wiki/Request_for_Comments

_List of RFCs_

https://en.wikipedia.org/wiki/List_of_RFCs