There are some variations on this practice. Some journals request open commentaries as a matter of course, which are published together with the original paper, and any authors' reply, in a process called open peer commentary. The introduction of the "epub ahead of print" practice in many journals now allows unsolicited letters to the editor (and authors' reply) to appear in the same print issue of the journal, as long as they are sent in the interval between the electronic publication of the original paper and its appearance in print.