I have just read about the architectural term tracery in the glossary of essential information in Chapter 16, “The arts”, of the section THE STUDY OF MAN in Volume 2, THE HUMAN WORLD, of the Reader’s Digest Library of Modern Knowledge.
I bet Catherine Morland saw a lot of the ornamental stonework in the Gothic windows of Northanger Abbey when she visited the place. Then again maybe she was too preoccupied with looking for dark adventures there to notice.