A limerick is a form of poetry, especially one in five-line meter with a strict rhyme scheme (AABBA), which is sometimes obscene with humorous intent. The first, second and fifth lines are usually longer than the third and fourth. The oldest attested text in this form is a Latin prayer by Thomas Aquinas of the 13th century. The form appeared in England in the early years of the 18th century. It was popularized by Edward Lear in the 19th century, although he did not use the term. The following limerick is of unknown origin: Gershon Legman, who compiled the largest and most scholarly anthology, held that the true limerick as a folk form is always obscene, and cites similar opinions by Arnold Bennett and George Bernard Shaw, describing the clean limerick as a “periodic fad and object of magazine contests, rarely rising above mediocrity.” From a folkloric point of view, the form is essentially transgressive; violation of taboo is part of its function.