A few questions explicitly ask for a solution where the editor performs the task itself without having to resort to external filters/tools. This is either in the main body of the question or in a comment. For example:
Some just have a preference to not using an external tool, for example:
I thought I'd seen more in the past, but the above come up in a quick search for me.
Some comments have pointed out that it is better to not restrict the question to pure Vi[m], since solutions with external tools allow for a better variety of answers that can help a broader scope of people.
On the other hand, some OP's need an answer with the restriction as they can be on a computer that lacks those external tools and also lack the privileges to install additional software.
A secondary question, if we decide this tag is a good idea, is what label to use. Saying something like pure-vi would seem to exclude other family editors (unless we had a pure-* tag for each editor). internal doesn't seem very descriptive of this intent. I can't think of other names.