The MLA Style center writes:
The concept of containers is crucial to MLA style. When the source being documented forms part of a larger whole, the larger whole can be thought of as a container that holds the source.
If your reader must access a whole resource in order to view the part you are referring to, you must refer to the whole in your works cited entry. This 'whole' is called the container in MLA Style. Examples of resources that will have containers include an ebook accessed through a database, a chapter in a book, or a post on a website.
Additionally, sources may have more than one container, such as an article contained in journal, contained in an online database.
Journal Article from an Online Database
Williams, Megan. "Breast Cancer and the Environment." Canadian Woman Studies, vol. 14, no. 3, 1994, pp. -10. Canadian Business and Current Affairs, search.proquest.com/docview/217458520?accountid=37666.
This Journal article has two containers. the database Canadian Business and Current Affairs contains the journal Canadian Woman Studies, which contains the article "Breast Cancer and the Environment".
Chapter from an Edited Book
Hesse, Carla. "Books in time." The Future of the Book, edited by Geoffrey Nunberg, U of California P, 1996, pp. 21-36.
The book The Future of the Book, edited by Geoffrey Nunberg, contains the chapter "Books in time", writtenby Carla Hesse
Post on a Website
Carillo, Ellen. "Digital Literacy in 'Post-Truth America' : An Interview." MLA Style Center, Modern Language Association, 31 July 2018, style.mla.org/digital-literacy.
the website MLA Style Center contains the post "Digital Literacy in 'Post-Truth America'"