function linenumber(event) {
    if (this.className == "hl-main ln-hide") {
        this.title = "Double click to hide line number.";
        this.className = "hl-main ln-show";
    } else {
        this.title = "Double click to show line number.";
        this.className = "hl-main ln-hide";
    }
}

var codes = document.getElementsByTagName('ol');
for (i = 0; i < codes.length; i++) {
	if (codes[i].className == "hl-main") {
        codes[i].title = "Double click to hide line number.";
        codes[i].className = "hl-main ln-show";
		codes[i].ondblclick = linenumber;
		
	}
}