Basically if you were the last one to make a post in a thread and attempt to do so again by default the post will be merged with the earlier one. Green text will appear to notify the difference in time between the original and the addition. For example, if done 5 minutes later it will state this. Below is an example.
Right now there is still an option to check to make it be a separate post rather than merged with the latter, which should cater some of the fan fiction stuff which might hit character limits on posts.
