Parenthetical/nonessential/non-restrictive commas are proving to be the bain of my life atm.
My first question is whether they are all names relating to the same idea? Non-restrictive modifiers, for instance, always describe either a noun or verb of the sentence, yet words that are interjected into the sentence are said to have no grammatical relation to anything else. When speaking in the vocative, as well, or enclosing apoosited dates/geographical locations, some style guides recommend treating these as parentheticals; however, they seem to be functioning differently from modifiers, no? Can these interruptions or asides be almost anything, so long as they are fragments and don't contain a subject-verb agreement?
Secondly, are introductory words, phrases, and clauses also considered nonessential modifiers/parentheticals when separated by a single comma? Sometimes they contain the important info. and then a pronoun steps in as the main clause's subject.
Is it acceptable to place any type of parenthetical at the end of the sentence? It's common to see nonessential appositives or non-restrictive modifiers following the main clause, but less common to see interjections, for instance.
finally, why is it acceptable to have one nonessential being nonessential to another nonessential, which itself might be acting this same way to the main clause, as in this sentence: The bike store included the later models, including the 9400x, which itself had state of the art tyres." The second dependent clause is functioning as a nonessential to the first nonessential, right? Could this pattern be repeated ad infinitum?
Apologies for the length, and thanks in advance for any responses.