The word ‘doublure’, a French word meaning a lining, which has been used rather indiscriminately of almost any decorated material on the inside of the boards of a book, is problematic in the description of a binding, as although it is often used, it has been used to mean a variety of different components and it does not in itself define a binding component so much as a rather vague concept, different manifestations of which can be found in the same place, i.e. on the inside of the boards of a binding. They may be endleaves used as pastedowns, even if made of tanned skin and often, but not always, decorated with tooling, or separate pastedowns (which might be described as linings) or even comb lining extensions cut to extend across the full width of the board. However they are made, the word is frequently used to imply a degree of applied decoration on the material used or the use of an exotic material such as watered or decorated silk, snake-skin, etc. How much decoration and what type of material is required to turn a pastedown into a ‘doublure’ is an open question, and it can be argued that it is therefore best to restrict a description to the technical facts (‘pastedown of tanned skin with gold-tooled borders’, ‘separate pastedown of watered silk with a joint of tanned skin’, ‘full-width comb-lining extension of red, tanned goatskin with a gold-tooled border frame’, etc.) rather than take a chance on the word ‘doublure’, the chance lying in whether both the writer and reader of a description will have the same definition in mind. If the word 'doublure' is used, it should always, wherever possible, be qualified by the component or components from which it is made.
Broader partitive concept: