MLA Style Center - Optional Elements: A PrimerWorks-cited-list entries in MLA style are based on the template of core elements. Sometimes, however, you may want or need to give your reader additional information about the source you’re documenting. You can do so by adding optional-element slots to the template. This post expands on the advice given in the MLA Handbook (50–53) and explains how and when to use the optional-element slot.
Optional-element slots are almost always inserted after the author-title unit or at the end of an entry. Since information in works-cited-list entries points back to what precedes, where you place it will depend on whether it pertains to the entire work or just to one element in the entry.