§ 187 Arrest made by whom.

Here's a plain English summary of this rule:

An arrest can happen in three different ways. First, a police officer can arrest someone when they have a warrant, which is a written order from a judge allowing the arrest. Second, a police officer can arrest someone without having a warrant first, as long as the situation allows for it. Third, in some cases, a regular private citizen can also make an arrest.

This rule matters because it shows that arrests are not limited to just police officers with warrants in hand. If you are stopped or detained by law enforcement, they may not always have a warrant, and the law still allows this in certain situations. It also means that under specific circumstances, another person besides a police officer could legally detain someone, though this is less common and usually comes with stricter limits.