Hi, 

You can refer as below if you want to retrieve myProperty from myPage in your custom control.

<pega:reference name="myPage.myProperty" />

But, If you want to Pass Page name dynamically as String param to your custom control, you can use java tags to fetch values from it.

<%
String Page="pyWorkPage";
String CaseID=tools.findPage(Page).getString(".pyID");
%>
  
<h2>Case ID : <%=CaseID %> </h2>

In the above example, We have passed Page value dynamically from a String.

<%
String Page=tools.getParamValue("PAGE_PARAM");
String CaseID=tools.findPage(Page).getString(".pyID");
%>
  
<h2>Case ID : <%=CaseID %> </h2>

If you want to use Param inside your custom control, you can use the above code.

I hope it helps you a bit.

Good Luck!