What does it mean if a function's toString() starts with "bound: "?
<p>In the chrome developer console, type <code>$x.toString()</code> (<code>$x</code> is one of the built-in functions of the dev tools console). The output looks like this:</p>

<pre><code>"bound: function (xpath, context)
    {
        var doc = (context &amp;&amp; context.ownerDocument) || inspectedWindow.document;
        var result = doc.evaluate(xpath, context || doc, null, XPathResult.ANY_TYPE, null);
        switch (result.resultType) {
        case XPathResult.NUMBER_TYPE:
            return result.numberValue;
        case XPathResult.STRING_TYPE:
            return result.stringValue;
        case XPathResult.BOOLEAN_TYPE:
            return result.booleanValue;
        default:
            var nodes = [];
            var node;
            while (node = result.iterateNext())
                nodes.push(node);
            return nodes;
        }
    }"
</code></pre>

<p>What is the meaning of "bound: ", in the first line?</p>
