javascript - 引入的@font-face的时候，为什么src属性值中要加入local方法？

@font-face {
font-family: 'Quattrocento';
font-style: normal;
font-weight: 400;
src: local('Quattrocento'), url(http://fonts.gstatic.com/s/qu... format('truetype');
}
@font-face {
font-family: 'Quattrocento';
font-style: normal;
font-weight: 700;
src: local('Quattrocento Bold'), local('Quattrocento-Bold'), url(http://fonts.gstatic.com/s/qu... format('truetype');
}