getSlideNotes( slide = this.Reveal.getCurrentSlide() ) {

		// Notes can be specified via the data-notes attribute...
		if( slide.hasAttribute( 'data-notes' ) ) {
			return slide.getAttribute( 'data-notes' );
		}

		// ... or using <aside class="notes"> elements
		let notesElements = slide.querySelectorAll( 'aside.notes' );
		if( notesElements ) {
			return Array.from(notesElements).map( notesElement => notesElement.innerHTML ).join( '\n' );
		}

		return null;

	}
Retrieves the speaker notes from a slide. Notes can be
defined in two ways:
1. As a data-notes attribute on the slide <section>
2. With <aside class="notes"> elements inside the slide

@param {HTMLElement} [slide=currentSlide]
@return {(string|null)}