So, each multiview component represents one article in the CMS. And each article in the CMS is represented by a domain object, with various fields for the article name, date, etc... as well as a field for HTML content. Hence the HTML content shown in the HTML tab of the multiview component should NOT come from an actual HTML file on disk. Instead, the NetBeans MemoryFileSystem should be used, while the features of the NetBeans HTML Editor should be made available for that specific field in the domain object.
After help from Vita Stejskal from the NetBeans editor team, everything is now working as expected:
To illustrate the point, I even integrated the NetBeans Groovy editor into the multiview component, within a new tab:
And one of the best things about it is that each tab is provided by a different module. Handy for the developers, handy for the end users, and handy for the pricing structure of the application.
Complete sources: cms.zip