In the code editor, look at the property on MessageDisplayer's propTypes object:

message: React.PropTypes.string

What are the properties on propTypes supposed to be, exactly?

The name of each property in propTypes should be the name of an expected prop. In our case, MessageDisplayer expects a prop named message, so our property's name is message.

The value of each property in propTypes should fit this pattern:

React.PropTypes.expected-data-type-goes-here

Since message is presumably going to be a string, we chose React.PropTypes.string. You can see this on line 7. Notice the difference in capitalization between the propTypes object and React.PropTypes!

Each property on the propTypes object is called a propType.

Select the next file in code editor, Runner.js. Find Runner's propTypes object.

Runner has six propTypes! Look at each one. Note that bool and func are abbreviated, but all other datatypes are spelled normally.

If you add .isRequired to a propType, then you will get a console warning if that prop isn't sent.

Try to find all six props from the propTypes object in Runner's render function: this.props.message, this.props.style, etc.