This page is a good starting point. But I will need some additional doc while customizing sections. I downloaded a skin form https://skins.wmflabs.org/#/add. On the template `ContentNamespaces.mustache` it contains the following line, how do I know what data it contains or how can i edit the list items?
{{#data-portlets.data-namespaces}}{{>Portlet}}{{/data-portlets.data-namespaces}}