The category I'm thinking of is a subset of self-referential; a concept which is encapsulated in its expression, where it is an example of itself: "This is a sentence" or "is sentence fragment" or `<html>`. It's an admittedly fuzzy/arbitrary category that I made up. :)
Is the word "non-self-referential"
self-referential?
Is it non-self-referential?
> shibboleth" works perfectly well as a shibboleth
You know why that is, right? The concept is named after the use of the word.