[For more current case annotated texts by this author, see Bernstein & Lookofsky, Understanding the CISG in Europe, 2d ed. (2003) and Lookofsky, Understanding the CISG in the USA, 2d ed. (2004).]
264. A buyer may wish to enter a binding contract to purchase goods (e.g. sweaters) even though she is, at the time of contracting, as yet undecided about the precise specifications of the goods she intends to buy: sizes, colours, etc. In this [page 139] case, the contract can provide that the buyer will provide such specifications in due course. If the buyer then fails to make such specification either on the date agreed upon or within a reasonable time after receipt of seller's request, the Convention permits the seller to make the specification himself. The seller must then inform the buyer of the details thereof and must also fix a reasonable time within which the buyer may make a different specification. If the buyer fails to do so, the specification made by the seller is binding.
Such specifications will be significant if, as is likely, the buyer proceeds to breach the contract in other respects, e.g., by failing to pay, take delivery, etc. Once the goods are specified, the contract cannot be declared 'void for vagueness,' and the seller who is entitled to avoid  will then be able to resell to another buyer and use the resale price as a means of calculating damages for breach.