MLA Handbook, 8th edition, asks writers to consider containers when creating citations. Containers normally appear in italics. They are followed by a comma because everything that comes after a container title--editor and other contributors, publisher name, date of publication, and page numbers--describes the container (30). Many MLA citations will include one or two discrete containers.
Types of Containers
A source is a segment of a container. "Use quotation marks for the titles of sources that are contained in larger works. Follow a source with a period" (68).
Types of Sources
Important Exception: MLA 8th still expects writers to "italicize titles of sources that are self-contained and independent" (68). Therefore, italicize book and film titles even when they are not containers, but place a period after them.
MLA Handbook. 8th ed., Modern Language Association of America, 2016.