Twitter just rolled out a sweet new mini-feature, retweet with comment, which essentially allows users to embed and comment on a tweet within another tweet, like this:
What this means is that users now have the option to add a comment right as they hit retweet:
Previously, if you wanted to append a comment to a tweet, you either had to manually copy-paste its permalink into a new tweet, or you had to copy-paste the text of the tweet and squish your comment into however many characters you had left over: