in js/reveal.js [4997:5025]
function navigateNext() {
hasNavigatedRight = true;
hasNavigatedDown = true;
// Prioritize revealing fragments
if( nextFragment() === false ) {
var routes = availableRoutes();
// When looping is enabled `routes.down` is always available
// so we need a separate check for when we've reached the
// end of a stack and should move horizontally
if( routes.down && routes.right && config.loop && Reveal.isLastVerticalSlide( currentSlide ) ) {
routes.down = false;
}
if( routes.down ) {
navigateDown();
}
else if( config.rtl ) {
navigateLeft();
}
else {
navigateRight();
}
}
}