I would like to write an article on overview of portlets.
I have read the JSR 168 document for the purpose of writing this article. In addition, I have done internet search on this subject and I found information about the concept of 'concrete-portlet' and related topics.
I have some problems to understand the concept of 'concrete-portlet', which is not specified in the JSR 168 document.
I am wondering if the concept of 'concrete-portlet' is related to a specific portal provider. If not, why is there no information about this concept in the JSR 168 document?
Do you know where I could find more information about this subject?