Why Can WebMethod Access Session State Without EnableSessionState?

Question

I have a method on a page marked as a [WebMethod] that uses some session state as part of its operation. After I wrote this code, I suddenly had a flash of memory that you need to use EnableSessionState when you use session state in a [WebMethod] (e.g. see here: http://msdn.microsoft.com/en-us/library/byxd99hx.aspx). But it seems to be working fine. Why?

Sample code behind:

protected void Page_Load(object sender, EventArgs args) {
    this.Session["variable"] = "hey there";
}
[System.Web.Services.WebMethod]
public static string GetSessionVariable() {
    return (string)HttpContext.Current.Session["variable"];
}

Sample body html:

<script src="Scripts/jquery-1.4.1.min.js" type="text/javascript"></script>
<script type="text/javascript">
    function getSession() {
        $.ajax({
            type: 'POST',
            url: 'Default.aspx/GetSessionVariable',
            data: '{ }',
            contentType: 'application/json; charset=utf-8',
            dataType: 'json',
            success: function (msg) {
                document.getElementById("showSessionVariable").innerHTML = msg.d;
            }
        });
        return false;
    }
</script>
<form id="form1" runat="server">
    <div id="showSessionVariable"></div>
    <button onclick='return getSession()'>Get Session Variable</button>
</form>

Answer 1

On http://msdn.microsoft.com/en-us/library/system.web.services.webmethodattribute.enablesession(v=vs.90).aspx, you will see that this applies to XML Web services (i.e., classes derived from System.Web.Services.WebService).

[WebMethod(EnableSession=true)]

Because your page presumably extends System.Web.UI.Page, it is not necessary to explicitly enable the session. On http://msdn.microsoft.com/en-us/library/system.web.configuration.pagessection.enablesessionstate.aspx, you can see that EnableSessionState is enabled by default for Pages (which you probably already know).