In a sentence beginning, "The head officer[,] or his designee[,] shall..." are the bracketed commas appropriate? If so, could you explain the formal grammar rule that would require them? I'm a legal proofreader; if I suggest commas, it must be ascribed to a formal grammar rule, rather than personal choice. (And as a bonus question, is the comma I placed before "rather" necessary?)
The discussion, both in the previous answers and the commentary, raises some interesting points about punctuation in general and the use of commas in this particular case. The OP has asked about a "formal grammar rule," and one respondent has declared himself a syntactical purist while talking about a "hard and fast rule." There's been mention of "speaking" and "saying."
At the risk of becoming hackneyed, let me repeat the instruction that
punctuation is a matter of style for written text, and as such you should be guided by your manual of style.
First, this means that punctuation rules aren't a matter of grammar in say, the way of the English grammar rule that the passive voice of a verb is made with an auxiliary form of "to be" and the past participle of the verb in question. Punctuation exists to guide readers into making the correct syntactic choice in parsing sentences. The reason is that English syntax is a recursive, tree-like creature, and ambiguity arises when we force it into linear text. (Note that I wrote "readers": there is no oral punctuation except in a Victor Borge comedy routine, which I have referenced before.)
Manuals of style issue many seeming diktats but temper them with the reservation that the writer has the ultimate choice. As the Chicago Manual of Style notes in its thirteenth edition in the introduction to its nearly 20 different rules for the use of the comma,
There are a few rules governing ... [the comma's] use that have become almost obligatory. Aside from these, the use of the comma is mainly a matter of good judgment.
But there are many competing manuals of style, and they don't always agree. Not only that, but as the CMS notes there are changing styles of style. An older version, so-called close punctuation follows the grammar more closely than more contemporary, open punctuation.
Let's (finally) examine the aptness of the commas in
The head officer[,] or his designee[,] shall ...
I will be guided by CMS, which says that generally commas are not to separate two compound subjects. And there's another reason to omit the commas: as has been noted in this discussion, non-restrictive appositives (i.e., renamings) are set off by commas and these can be disguised by the word or:
The bubonic plague, or the "Black Death", ....
Using the commas thus may make it difficult for readers to discern at first glance whether there are one or two people authorized to do what they shall do. But the comma cannot take the weight of determining that the or is exclusive, that the designee operates only in the absence of the chief officer. Perhaps that's what the company's by-laws say, but that's not how a power of attorney operates. And a comma isn't up to the task of telling how things work.
But there's another (and naturally, contradictory) consideration from CMS -- asides or parenthetical elements are generally set off by commas:
The head officer, as long as he is mentally competent, ....
Is the alternative of the designee an aside and thus worthy of accompanying commas? It's impossible to tell without more context. If this fragment is from a discussion of the powers of the head officer, maybe so. If it's a reminder about the duties of designees, perhaps not.
If manuals of style cannot settle issues of punctuation with finality, then why use them? I can think of two reasons. First, if you write for someone else, be it thesis advisor or employing organization, a manual of style may be thrust upon you. Secondly, even if you're free to write as you please, a manual of style will help keep your punctuation consistent. Your readers may well adapt to an idiosyncratic style, but not if they can't tell what it is from paragraph to paragraph.
Finally, should there be a comma before "rather" in the OP. Well, CMS says to set off complementary or contrasting items, here "formal" on the one hand and "personal" on the other. But, all together now,
It's a matter of style.
The sentence has multiple subjects and a single verb. There is no reason why the bracketed commas should be included; in fact, it is erroneous to add them. The format of the sentence is no different than if it was:
The head officer and his designee shall...
The fact that the conjunction used is an "or" does not change the punctuation rule.
If it is used as an appositive, meaning the phrase within the commas is equivalent to the phrase directly before it, the commas would be necessary. e.g:
Thomas, the head officer, shall...
The head officer, or "chief," shall...
In the first example, it is clarifying a specific person's role as head officer. In the second, it is ascribing a particular title to the position of head officer. In both, the phrase within the parentheses is a clarification of the phrase before it and is referring to the same noun. Both need the pair of parentheses
However, in your context, no parentheses should be added.
NOTE: Sorry if I offend you with my blatant misuse of your example out of context. Pay attention only to the syntactical arrangement of my examples.
You need formal style where things are not to be the subject of opinions, feelings, considerations.
The reason you may or may not use comma is that it is a matter of style. Formal style is the one that says that you do not have this freedom.
In your case not using comma may suggest whoever is present at the time. With comma it could mean preceding: if the head officer is there then he is to do something, only if he is incapacitated then his designee can do it. For this reason I would add instead, for example. Another confusion is how many people can be a designee. Without comma it is suggesting one, with comma anyone that is a designee.
All this should be specified, not left to the interpretation of comma.