Why are optional elements now called supplemental elements?

The ninth edition of the MLA Handbook simplifies and clarifies the terminology used to describe some of the elements of a works-cited-list entry.

In MLA style, works-cited-list entries are created using a template of core elements. But on occasion it might be necessary or useful to supply other details about a source. In the previous edition, these elements were called optional elements. But since this information is sometimes required (as in example 1 below) and other times optional (as in example 2 below), the ninth edition uses the term supplemental elements to describe it.

Example 1: A Required Supplemental Element 

Translators play an important role in a work, so their names must be provided in the works-cited-list entry for a translation. In the entry below, Leila El Khalidi and Christopher Tingley are not listed in the Contributors element because they did not translate all the plays in Short Arabic Plays. They translated The Singing of the Stars, so their names are given in the middle supplemental element after the title of the play.

Fagih, Ahmed Ibrahim al-. The Singing of the Stars. Translated by Leila El Khalidi and Christopher Tingley. Short Arabic Plays: An Anthology, edited by Salma Khadra Jayyusi, Interlink Books, 2003, pp. 140-57.

Example 2: An Optional Supplemental Element

Sometimes a section of a work has both a unique title and a generic label. If you think the generic label will provide important information to your reader, you can supply it in the middle supplemental element, but this information is optional. The entry below shows the generic label Introduction in the middle supplemental element after the unique title.

Seyhan, Azade. “Novel Moves.” Introduction. Tales of Crossed Destinies: The Modern Turkish Novel in a Comparative Context, Modern Language Association of America, 2008, pp. 1-22.