PRIMEDIA is the vast, ever-expanding pool of media resources available on the network. This may be plain text, raster images, audio and video streams, or any other imaginable type of media.

Primedia must be address-stable, and content-stable.

When a resource is published to the network at a certain address, it should remain available at that address forever – or, a seamless and reliable redirection mechanism must exist for moved resources.

And, once published to the network, a resource's contents should not change in a way that effects the deep-addressing of its content. We'll come back to this point in a moment.

Primedia must be deeply-addressable.

It is not sufficient that a resource be addressable in its entirety by name; rather, a mechanism must exist by which a fragment of the resource can be directly addressed, i.e.: a substring of a plain-text, a cropped portion of an image, a clip of an audiovisual recording, and so-on.

For example, let's say that we have a plain-text resource at the following URL: https://example.site/resource.txt

And that text's contents are this:

https://example.site/resource.txt
---------------------------------
Hello, world!

If we wanted to refer specifically to the word "world" in that text, we could use a simple numeric fragment selector to point at the substring:

https://example.site/resource.txt#7-12
---------------------------------------
Hello, world!
       \---/---------------- "world"
       #7-12

Just in case that isn't clear, the numbers are pointing at the spaces between characters: before the H is index 0; before the W is index 7, and AFTER the D is index 12.

Now, if this resource were changed:

https://example.site/resource.txt
---------------------------------------
Hello there, world!

The address that we previously established as pointing to the word "world" now points to this instead:

https://example.site/resource.txt#7-12
---------------------------------------
Hello there, world!
       \---/----------------- "here,"
       #7-12

This kind of change should never happen to published primedia. New content should never be INSERTED into a resource, because it invalidates any reference to portions of the resource that lie beyond the point of change.

For the same reason, the contents of primedia should never be DELETED. If our original text were shortened after publication to simply "Hello!", then our reference would point to...

https://example.site/resource.txt#7-12
---------------------------------------
Hello!
       \---/------------------ nothing!
       #7-12

However, it is safe to APPEND to primedia[1]. If we restore our text resource to its original state, and then simply add more text to the end of it...

https://example.site/resource.txt#7-12
---------------------------------------
Hello, world! Call me Ishmael.
       \---/---------------------- still points to "world"
       #7-12

In the event that some part of a resource MUST be changed, the only way to do it so that address-stability is maintained is to OVERWRITE or redact information.

https://example.site/resource.txt#7-12
---------------------------------------
Hello, XXXXX! Call me Ishmael.
       \---/---------------------- [redacted]
       #7-12

Obviously, this is not ideal, but any references to other parts of the resource remain valid, and that's critical for the operation of a hypermedia system based on transclusion and linking-by-reference.

Here's a summary, just to drive the point home.

To maintain address-stability of primedia:

INSERT = BAD
DELETE = BAD
APPEND = OKAY
REDACT = NOT IDEAL, BUT YGDWYGD