He pointed out that the sandal-strap illustrations on Middle Kingdom coffins resemble the hieroglyph and argued that the sign originally represented knots like these and came to be used in writing all other words that contained the consonants Ꜥ-n-ḫ.[2] Gardiner's list of hieroglyphic signs labels the ankh as S34, placing it within the category for items of clothing and just after S33, the hieroglyph for a sandal.[14] Gardiner's hypothesis is still current; James P. Allen, in an introductory book on the Egyptian language published in 2014, assumes that the sign originally meant "sandal strap" and uses it as one of the major examples of the rebus principle in hieroglyphic writing.[4]