This summary is not the rule. The rule text controls.
Here's what this rule means for people involved in a children's court case.
The people involved in a case (called "parties") can agree in writing to change some of the normal rules about gathering evidence before trial. This process of gathering evidence is called "discovery." For example, they can agree on their own terms about who can take a deposition, and when, where, and how it happens. A deposition is when someone answers questions under oath before the trial, usually so their answers can be used as evidence later.
The parties can also agree in writing to change other discovery procedures, not just depositions. This gives everyone some flexibility to work out arrangements that make sense for their situation, instead of always following the standard court procedures.
There are limits, though. The court can still step in and order something different if needed. Also, if there is already a court order in place that conflicts with what the parties want to agree to, that existing order wins. So parties can work things out between themselves, but only within the boundaries the court allows.