found here:
https://docs.angularjs.org/api/ngAnimate

in this paragraph:
"CSS-based animations with ngAnimate are unique since they require no JavaScript code at all. By using a CSS class that we reference between our HTML and CSS code we can create an animation that will be picked up by Angular when an the underlying directive performs an operation."

The typo is where it says "an the." It should either say "an" or "the."