"Read" view of a file

[Sewi]

Add a main tab type (besides "editor") which doesn't allow editing a file but reading a project, for example for learning a project's source:

• Open a file (into this tab)
• Show the file contents
• on each sub/method call, show a "+" sign (maybe like the code folding option does)
• Clicking on this "+" shows the contents of the called sub (indented or colored) below the calling line
• This should work more than one level deep
• Double-clicking on a line opens a editor tab for this file and jumps to this line (like the Find-in-files feature)

This function should speed up the "work through a project to learn about it".

This is a request-for-comments idea, please discuss it and add your own ideas!