How can I setup the Layout parameter?
That option means if a template supports a custom layout for that menu item type, it will show there along with 'default' layout so you can select 🙂
How do I make a custom layout?
richnyc30 It depends on the menu item type that you're using for this menu item and customize associated component.
For example, with com_content, you can take a look at: root/templates/ja_blockk/html/com_content/
Is there a document?
I looked at the files, the php and xml, and I hope you don't think I can write script like this.
I can see the categories have the custom menu layouts and the others only have default.
Does a document say how to make a custom layout?
richnyc30 It's default feature of Joomla, you can make a search in Joomla forum for help on this.