Why this js code works?
<pre><code>if (!wysiwyg_toolbarButtons) {
    var wysiwyg_toolbarButtons = new Array(
        //command, display name, value, title, prompt/function, default text
        ["bold", "Strong", WYSIWYG_VALUE_NONE, "Give text strength"],
        ["italic", "Emphasis", WYSIWYG_VALUE_NONE, "Give text emphasis"],
        ["createlink", "Link", WYSIWYG_VALUE_PROMPT, "Create a hyperlink", "Enter the URL:", "http://"],
        ["unlink", "Unlink", WYSIWYG_VALUE_NONE, "Remove hyperlink"],
        ["insertimage", "Image", WYSIWYG_VALUE_PROMPT, "Insert an image", "Enter the URL of the image:", "http://"],
        ["inserthorizontalrule", "Rule", WYSIWYG_VALUE_NONE, "Insert horizontal rule"],
        ["div"], // place a toolbar divider
        ["formatblock", "Headling 1", "&lt;H1&gt;", "Make top level heading"],
        ["formatblock", "Headling 2", "&lt;H2&gt;", "Make 2nd level heading"],
        ["formatblock", "Headling 3", "&lt;H3&gt;", "Make 3rd level heading"],
        ["formatblock", "Paragraph", "&lt;P&gt;", "Make a paragraph"],
        ["formatblock", "Monospace", "&lt;PRE&gt;", "Make paragraph monospaced text"],
        ["insertunorderedlist", "List", null, "Make an unordered list"],
        ["insertorderedlist", "Ordered List", null, "Make an ordered list"],
        ["div"], // place a toolbar divider
        ["toggleview", "Source", "Compose", "Switch views"]
    );
}
</code></pre>

<p>It's from <a href="http://www.peej.co.uk/sandbox/wysiwyg/wysiwyg.js" rel="nofollow">this file</a>，with a demo <a href="http://www.peej.co.uk/sandbox/wysiwyg/" rel="nofollow">here</a></p>

<p>My problem is:why doesn't it report "ReferenceError: wysiwyg_toolbarButtons is not defined"?</p>
