This summary is not the rule. The rule text controls.
If someone in a court case shows only part of a document or recording, the other side can ask that the rest of it be shown too, right then and there. This stops people from taking a quote or a clip out of context to make it look better or worse than it really is.
For example, say a letter has five paragraphs, but one side only reads the second paragraph out loud because it helps their case. The other side can speak up and ask that the other paragraphs be read too, if leaving them out would give a misleading picture. The same goes for recordings, like an audio clip or video where only part of it gets played.
The idea behind this rule is fairness. Words and statements often make more sense, or mean something different, when you see or hear the whole thing instead of just a piece. This rule makes sure the judge and jury get the full picture at the same time, instead of hearing a one-sided version first and finding out the rest later.
