Formatting Titles: Italics v. Quotation Marks

Here is my statement of the general rule: Italicize the title of whatever is normally, or was in the first instance, published as a volume of its own. Obvious examples of the above:
--book titles
--movie titles

Put in quotation marks the title of whatever is normally part of something else, such as a collection of poems or an anthology.
Obvious examples of the above:
--chapter titles.
--a single poem from Sidney's Astrophil and Stella