Pobedill,
на всякий случай точка недопустимый символ в id ... и строка 50 только для теста
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<ul class="accordion">
<li class="accordion_item">
<label class="accordion_trigger" for="toggle-1">Заголовок 1</label>
<input type="checkbox" class="accordion_toggle" id="toggle-1" />
<div class="accordion_target">
<ul class="accordion">
<li class="accordion_item">
<label class="accordion_trigger" for="toggle-1.1">Заголовок 1.1</label>
<input type="checkbox" class="accordion_toggle" id="toggle-1.1" />
<div class="accordion_target">
<p>
Текст
</p>
</div>
</li>
<li class="accordion_item">
<label class="accordion_trigger" for="toggle-1.2">Заголовок 1.2</label>
<input type="checkbox" class="accordion_toggle" id="toggle-1.2" />
<div class="accordion_target">
<p>
Текст
</p>
</div>
</li>
</ul>
</div>
</li>
<li class="accordion_item">
<label class="accordion_trigger" for="toggle-2">Заголовок 2</label>
<input type="checkbox" class="accordion_toggle" id="toggle-2" />
<div class="accordion_target">
<p>
Текст
</p>
</div>
</li>
</ul>
<script>
window.addEventListener("load", function() {
var a = "#toggle-1.1"
//var a = location.hash;
a && (a = a.slice(1).split(".").reduce(function(b, a) {
b = b ? b + "." + a : a;
document.querySelector('[id="' + b + '"]').checked = !0;
return b
}, ""))
});
</script>
</body>
</html>