Tone
The writer's attitude toward the topic and the audience.
Resources
These two renditions of the Nat King Cole song "Miss Otis Regrets (she's be unable to lunch today)" illustrate a difference in tone:
"Natalie Douglas - 'Cafe Society' Miss Otis Regrets" 3:54 http://www.youtube.com/watch?v=7-UBSM6MsiE
"Bette Midler - Miss Otis Regrets" 2:34http://www.youtube.com/watch?v=qQnl4TX5wOE