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
public void addBufferChangedListener(IBufferChangedListener listener) {}
			public void append(char[] text) {}
			public void append(String text) {}
			public void close() {}
			public char getChar(int position) { return 0; }
			public char[] getCharacters() { return null; }
			public String getContents() { return null; }
			public int getLength() { return 0; }
			public IOpenable getOwner() { return null; }
			public String getText(int offset, int length) { return null; }
			public IResource getUnderlyingResource() { return null; }
			public boolean hasUnsavedChanges() { return false; }
			public boolean isClosed() { return false; }
			public boolean isReadOnly() { return true; }
			public void removeBufferChangedListener(IBufferChangedListener listener) {}
			public void replace(int position, int length, char[] text) {}
			public void replace(int position, int length, String text) {}
			public void save(IProgressMonitor progress, boolean force) throws JavaModelException {}
			public void setContents(char[] contents) {}
			public void setContents(String contents) {}
		}
		
		public final static IBuffer NULL= new NullBuffer();
		/**
		 *  Executes a document set content call in the UI thread.
		 */
		protected class DocumentSetCommand implements Runnable {