in js/reveal.js [2366:2397]
function navigatePrev({skipFragments=false}={}) {
// Prioritize revealing fragments
if( skipFragments || fragments.prev() === false ) {
if( availableRoutes().up ) {
navigateUp({skipFragments});
}
else {
// Fetch the previous horizontal slide, if there is one
let previousSlide;
if( config.rtl ) {
previousSlide = Util.queryAll( dom.wrapper, HORIZONTAL_SLIDES_SELECTOR + '.future' ).pop();
}
else {
previousSlide = Util.queryAll( dom.wrapper, HORIZONTAL_SLIDES_SELECTOR + '.past' ).pop();
}
// When going backwards and arriving on a stack we start
// at the bottom of the stack
if( previousSlide && previousSlide.classList.contains( 'stack' ) ) {
let v = ( previousSlide.querySelectorAll( 'section' ).length - 1 ) || undefined;
let h = indexh - 1;
slide( h, v );
}
else {
navigateLeft({skipFragments});
}
}
}
}