Can I update a component’s props in React.js?

After starting to work with React.js, it seems like props are intended to be static (passed in from the parent component), while state changes based upon events. However, I noticed in the docs a reference to componentWillReceiveProps, which specifically includes this example:

componentWillReceiveProps: function(nextProps) {
  this.setState({
    likesIncreasing: nextProps.likeCount > this.props.likeCount
  });
}

This seems to imply that the properties CAN change on a component based upon the comparison of nextProps to this.props. What am I missing? How do props change, or am I mistaken about where this gets called?