ngs [n1,delimiter,n2]. See #formatSlideNumber().
        slideNumber: {{ slide_number }},
        // Can be used to limit the contexts in which the slide number appears
        // - "all":      Always show the slide number
        // - "print":    Only when printing to PDF
        // - "speaker":  Only in the speaker view
        showSlideNumber: {{ show_slide_number }},
        // Use 1 based indexing for # links to match slide number (default is zero
        // based)
        hashOneBasedIndex: {{ hash_on