What is a writing, as the means of giving formal expression to some act; a writing expressive of some act, contract, process, as a deed, contract, writ, etc. Burrill called?

instrument — (Law) A writing, as the means of giving formal expression to some act; a writing expressive of some act, contract, process, as a deed, contract, writ, etc. Burrill. (Webster's 1913.)

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