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
fPath= fFile.getFullPath();
		initialize();
	}
	private void initialize() {
		ITextFileBufferManager manager= FileBuffers.getTextFileBufferManager();
		try {
			manager.connect(fPath, new NullProgressMonitor());
			fTextFileBuffer= manager.getTextFileBuffer(fPath);
			fDocument= fTextFileBuffer.getDocument();
		} catch (CoreException x) {
			fStatus= x.getStatus();
			fDocument= manager.createEmptyDocument(fPath);
		}
		fDocument.addPrenotifiedDocumentListener(this);
	}
	/**
	 * Returns the status of this document adapter.
	 */
	public IStatus getStatus() {
		if (fStatus != null)
			return fStatus;
		if (fTextFileBuffer != null)
			return fTextFileBuffer.getStatus();
		return null;
	}
	/**
	 * Returns the adapted document.
	 *
	 * @return the adapted document
	 */