A more thorough explanation:

The Doctrine of Optional Completeness is a rule of evidence that states when a party introduces part of a writing or an utterance at trial, the opposing party may require that the remainder of the passage be read to establish the full context.

For example, if a witness testifies about a conversation they had with someone, the opposing party can request that the entire conversation be read or played to the court to provide a complete understanding of the conversation.

However, there are limitations to this rule. The remainder of the utterance must explain the first part, and it must be relevant to the case. In some jurisdictions, the rule applies to conversations, an opponent's admissions, confessions, and all other types of writings, including account books. But in the Federal Rules of Evidence, the rule is limited to writings and recorded statements.

In most jurisdictions, including federal, the remainder is admissible unless its admission would be unfair or misleading.

Overall, the Doctrine of Optional Completeness ensures that the court has a complete understanding of the evidence presented and prevents any misleading or unfair interpretations.