What is the test for obtaining access to a copy of a document in a criminal case?

The prison might, for example, require a prisoner to make an affirmative request for access to evidence he may intend to use in his defense or that is expected to be used against him. The request need not be extremely detailed, particularly if the prisoner has no way of ascertaining or describing the precise form of the evidence he seeks, but it should be sufficient to put the prison official on notice of what is sought. Cf. Davis v. United States, 512 U.S. 452, 459 (1994) (holding that to invoke the right to counsel, a suspect must "articulate his desire to have counsel present sufficiently clearly that a reasonable police officer in the circumstances would understand the statement to be a request for an attorney"). For example, requesting the right to inspect a document should be understood to include the alternative of a copy of a document whether it be in the form of a photocopy, a photograph, or something else, unless the prisoner specifically indicates that only the original will do.