A more thorough explanation:

The optional-completeness doctrine, also known as the rule of optional completeness, is an evidentiary rule that allows a party to require the full context of a writing or utterance to be read when only part of it has been introduced as evidence in court.

For example, if a party introduces a portion of a conversation as evidence, the opposing party may request that the entire conversation be read to provide the full context. This rule applies to all types of writings, including account books, and recorded statements.

However, the rule has limitations. The remainder of the writing or utterance must explain the first part, and it must be relevant to the case. In most jurisdictions, the remainder is admissible unless its admission would be unfair or misleading.

For instance, if a defendant confesses to a crime but only a portion of the confession is introduced as evidence, the prosecution may request that the entire confession be read to provide the full context of the defendant's statement.

The optional-completeness doctrine is an important tool for ensuring that evidence is not taken out of context and that the full meaning of a writing or utterance is understood in court.