Finalizing image! as series (or not)
From reading the prior blog comments about what is and is not a series, I would propose the following:
I'd also propose we use some kind of simple test (just for deciding, not to add to mezz), such as:
is-series?: func [s] [(length? s) = (index? back tail s)]
This test implies that the index position exists, can propagate and be modified. (Hopefully, all existing series datatypes pass it.)
If you think this test is not valid, and that some other test should be used, then mention it now. We will be closing this issue in a day or so, and it will be more difficult to change later.