What does the three dots in react do?

http://stackoverflow.com/a/41640566/2177408

As you know ... are called spread operator which the name represents it allows an expression to be expanded.

var parts = ['two', 'three'];
var numbers = ['one', ...parts, 'four', 'five']; // ["one", "two", "three", "four", "five"]

And in this case(I'm gonna simplify it).

//just assume we have an object like this:
var person= {
    name: 'Alex',
    age: 35 
}

This:

<Modal {...person} title='Modal heading' animation={false} />

is equal to

<Modal name={person.name} age={person.age} title='Modal heading' animation={false} />

So in short, it's a neat short-cut, we can say.