The MHRA Style Guide Online
A Handbook for Authors and Editors • Third Edition
From Chapter 9, 'Quotations and Quotation Marks'
Quotation marks should normally be reserved for indicating direct quotations, definitions of words, or for otherwise highlighting a word or phrase. Avoid the practice of using quotation marks as an oblique excuse for a loose, slang, or imprecise (and possibly inaccurate) word or phrase.
Prose quotations of no more than forty words in a single paragraph or verse quotations of no more than two lines are considered short quotations, and are to be treated as in 9.3 below. All other quotations should be treated as long quotations, as in 9.4 below. If, however, several short quotations come close together and are compared or contrasted or otherwise set out as examples, it may be appropriate to treat them together as a long quotation.