I have a custom master page. When you create a custom master page then another page with similar name is automatically created by SharePoint.
For e.g. my master page name is mymaster.html so sharepoint created mymaster.master file with it. I want to increase the AsyncPostBackTimeout property of ScriptManager. I opened mymaster.html in SPD but didn't find any code there. Then I opened mymaster.master
in SPD and I can see the ScriptManager code written as below.
<asp:ScriptManager id="ScriptManager" runat="server" --more code here-- />
Problem is, SPD doesn't allow you to edit .master page and I can't add this code in my .html master page file. How to edit this code in SPD?