The chairman of the committee, Senator Jones, rambled on and on. The press surrounded the witness—the chief accuser of the candidate—as she exited the capital building. Her husband, David, accompanied her to the hearings.
His brother Tom came to dinner. The committee defined the term specifically by referring to the dictionary.
In the first example above, the restrictive appositive Tom, without commas, means that he has more than one brother. If he has just one brother, then the appositive is nonrestrictive and requires commas:
His brother, Tom, came to dinner.