Only one edit window! How do I create "Read more..."?

Only one edit window! How do I create "Read more..."?

This is now implemented by inserting a Read more... tag (the button is located below the editor area) a dotted line appears in the edited text showing the split location for the Read more.... A new Plugin takes care of the rest.

It is worth mentioning that this does not have a negative effect on migrated data from older sites. The new implementation is fully backward compatible.