ruby - Difference between ruby StringScanner post_match and rest?

Question

What is the difference between ruby's StringScanner#post_match and StringScanner#rest?

scanner = StringScanner.new('Say hello to...')
scanner.scan(/\w+/) #=> 'Say'
scanner.scan(/\s+/) #=> ' '
scanner.rest        #=> 'hello to...'
scanner.post_match  #=> 'hello to...'
scanner.rest.class  #=> String
scanner.post_match.class #=> String

I don't see a difference. It seems like both return a string containing everything after the match.