<rendering:placeholder id="contentplaceholder"/> will never work in MasterPages, that is a XML template specific tag.
The section you referred to explained how to find the ID's of ones placeholders in the template, so whats what i answered. If you need to know how to render as placeholder in as MasterPage its well documented here http://docs.composite.net/Layout/Master-Page-Templates/Adding-Placeholders
The section you referred to explained how to find the ID's of ones placeholders in the template, so whats what i answered. If you need to know how to render as placeholder in as MasterPage its well documented here http://docs.composite.net/Layout/Master-Page-Templates/Adding-Placeholders