I just realized you can simplify the regular expression even further.
Let's say you have the string "aaa-bbb". The first "a" obviously matches the character class [a-z], and the second "a" matches the character class [a-z ' -]. There is absolutely no way to tell if the third "a" matches the [a-z ' -] of the old group, or the [a-z] of a new group.
This means that the following regular expression matches the same strings as your original: