Sometimes I have to work with class files that are necessarily large (2000-lines) and have many facets: a static side and an instance side.  In addition there 
may be 50 or so member variables, plus sometimes a few small inner classes.  Each of these parts is somewhat separate.  For example, the static methods 
are almost in a world to themselves compared to the instance methods, and the member are conceptually separate from the methods that may act on 
them.  

Navigating through these different "worlds" within one source file is a challenge.  Eventually I (and I'm sure everyone else) develop a style that helps.  For 
example I keep all members at the top, then static methods, then instance, then classes.  Sometimes I use lines of //// characters to separate sections.  But 
all this is only somewhat helpful, and I sometimes get lost in the worlds between static and instance, or I confuse an inner class's methods with the 
parent's.  And lots of scrolling around is tiresome too.

My idea is to have the IDE separate these parts into subtabs when editing a source file.  I'm imagining tabs with the names: "Imports", "Static Members", 
"Instance Members", "Static Methods", "Instance Methods", "<name> Inner Class"

On opening, the IDE would scan the source file and build the subtabs automatically.  On saving it would put the pieces back together in a "standard" way.  
Of course this starts to sound intrusive (like old GUI builder tools), but I think it would be so coarse that it wouldn't step on a developer's toes too much... it 
would have no effect on method ordering, indent style, documentation, etc. within each subtab.  The only adulteration would occur when the subtabs are 
combined into a single source file.  (It may be possible to edit the source file in the background with minimal reordering, like a diff... but that is beyond my 
expertise to be certain.)

If nothing else, this arrangement would save a lot of bookmarking and scrolling.  How many times have you had to scroll to the top to look at a member, 
then scroll back down to a method?  That scrolling back and forth would be eliminated if each section could be focused in a separate tab.

If the scheme works, then the next step might be to show the tabs in separate frames within the window.  (Especially with larger screens becoming 
affordable today.)