I commonly see commas used like: "The famous playwright, William Shakespeare, was born in Stratford-upon-Avon."
It bothers me, but I'm curious to hear explanations of why this is done, and if it can be considered correct English. Is there any style manual that approves?
I would accept "The famous playwright William Shakespeare was born in Stratford-upon-Avon" or "William Shakespeare, the famous playwright, was born in Stratford-upon-Avon".
However, when phrased like "The famous playwright, William Shakespeare, was born in Stratford-upon-Avon", I read the name as parenthetical. But that sentence doesn't make a lot of sense with the name removed, as "the famous playwright" looks definite, but is undefined.
It suppose it could make sense in a context where the subject is mentioned previously, something like "Once upon a time, there was a well-known dramatist. The famous playwright, William Shakespeare, was born in Stratford-upon-Avon." In that case, the name really is parenthetical. But I've seen commas used this way without such a context, and often, I believe, in the very first sentence of a text.