PlaceHolder inside ContentPlaceholder

Why is it not possible to access PlaceHolder control from cs file, which is placed in ContentPlaceHolder aspx page in the Content section?
<%@ Page Language="C#" MasterPageFile="~/MasterPage.master" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" Title="Untitled Page" %>
<asp:Content ID="Content1" ContentPlaceHolderID="ContentCategories" runat="Server">
<ASP:DataList id="CatDataList" RepeatColumns="1" runat="server">
        <table cellpadding="10" style="font: 10pt verdana">
            <td valign="top">
              <b>Category: </b><%# DataBinder.Eval(Container.DataItem, "CategoryName") %> <br /> <br />
              <asp:PlaceHolder ID="phGridProject" runat="server"> </asp:PlaceHolder>                       

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It's because you have it nested in a DataList ItemTemplate.
VonGuntenAuthor Commented:
Ok, but how to reach it?

I tried with:
PlaceHolder ph1 = ((PlaceHolder)CatDataList.FindControl("phGridProjects"));

but when I try to add a control to ph1 there is an exception thrown that the reference is not set to an instance of an object.

How to reach this PlaceHolder.
VonGuntenAuthor Commented:
One more thing. I try to reach it in inside of OnItemDataBound method.
VonGuntenAuthor Commented:
Ok. I got it. It has to be:

 PlaceHolder ph1 = ((PlaceHolder)e.Item.FindControl("abc"));

Thanks anyway

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