Bug 96917 [implementation] If two editors use the 2.x-compatible API, one or both doesn't work
At least one problem is that 3.0 installs partitioners for every editor that might possibly edit a file, but each editor expects its own partitioner to be installed. Leading to the famous white screen with blue line.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/DocumentAdapter.java
private void validateLineDelimiters(String contents) {
		if (fLegalLineDelimiters == null) {
			
			HashSet existingDelimiters= new HashSet();
			for (int i= fDocument.getNumberOfLines() - 1; i >= 0; i-- ) {
				try {
					String curr= fDocument.getLineDelimiter(i);
					if (curr != null) {
						existingDelimiters.add(curr);
					}
				} catch (BadLocationException e) {
					JavaPlugin.log(e);
				}
			}
			if (existingDelimiters.isEmpty()) {
				return; 
			}
			fLegalLineDelimiters= existingDelimiters;
		}
		DefaultLineTracker tracker= new DefaultLineTracker();
		tracker.set(contents);
		int lines= tracker.getNumberOfLines();
		if (lines <= 1)
			return;
		for (int i= 0; i < lines; i++) {
			try {
				String curr= tracker.getLineDelimiter(i);
				if (curr != null && !fLegalLineDelimiters.contains(curr)) {
					StringBuffer buf= new StringBuffer("New line delimiter added to new code: "); 
					for (int k= 0; k < curr.length(); k++) {