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.
