This summary is not the rule. The rule text controls.
When an expert witness testifies in court, they don't have to walk through all the background facts and data before sharing their opinion. They can simply state their opinion and explain their reasoning right away. This makes things move faster and keeps the testimony more direct.
However, the other side's lawyer can still ask about the underlying facts and data during cross examination. So if a lawyer wants to challenge the expert's opinion or see what it's based on, they have the chance to dig into that information later in questioning. A judge can also step in and require the expert to explain their facts and data upfront, if the judge thinks that's necessary.
This rule basically lets expert testimony flow more smoothly at first, while still giving both sides a chance to fully examine the reasoning behind an expert's conclusions.
