diff --git a/repository/BaselineOfOpenPonk/BaselineOfOpenPonk.class.st b/repository/BaselineOfOpenPonk/BaselineOfOpenPonk.class.st
index 33073aae..0798e562 100644
--- a/repository/BaselineOfOpenPonk/BaselineOfOpenPonk.class.st
+++ b/repository/BaselineOfOpenPonk/BaselineOfOpenPonk.class.st
@@ -1,6 +1,6 @@
 "
-I am baseline for the core and all-in-one dynacase.
-https://dynacase.github.io/
+I am baseline for the core of Openponk.
+https://openponk.org/
 "
 Class {
 	#name : 'BaselineOfOpenPonk',
@@ -37,7 +37,7 @@ BaselineOfOpenPonk >> externalProjectsBaseline: spec [
 	spec
 		baseline: 'XPath'
 		with: [
-		spec repository: 'github://pharo-contributions/XML-XPath:2aa720c' ].
+		spec repository: 'github://pharo-contributions/XML-XPath:v2.3.x' ].
 
 	spec baseline: 'Magritte' with: [
 		spec
diff --git a/repository/OpenPonk-Core/OPController.class.st b/repository/OpenPonk-Core/OPController.class.st
index c7d86a0d..64dd40e8 100644
--- a/repository/OpenPonk-Core/OPController.class.st
+++ b/repository/OpenPonk-Core/OPController.class.st
@@ -364,3 +364,9 @@ OPController >> updateAfterDiagramFocused [
 
 	self subclassResponsibility
 ]
+
+{ #category : 'validation' }
+OPController >> validate [
+
+	"do nothing by default"
+]
diff --git a/repository/OpenPonk-Core/OPDiagramController.class.st b/repository/OpenPonk-Core/OPDiagramController.class.st
index 6bc5baf6..1fa94ff7 100644
--- a/repository/OpenPonk-Core/OPDiagramController.class.st
+++ b/repository/OpenPonk-Core/OPDiagramController.class.st
@@ -760,7 +760,8 @@ OPDiagramController >> showDiagramElement: aDiagramElement [
 				              ifFound: [ :ctrl |
 					              ctrl isRendered ifTrue: [
 						              aDiagramElement isRendered ifTrue: [ ^ ctrl ].
-						              ^ self error: 'Controller is already rendered' ].
+						              ^ self error:
+							                'Controller is already rendered by a different diagram element' ].
 					              ctrl ]
 				              ifNone: [
 				              self newControllerFor:
@@ -840,6 +841,12 @@ OPDiagramController >> updateView [
 	^ self updateCanvas
 ]
 
+{ #category : 'validation' }
+OPDiagramController >> validate [
+
+	self controllers do: [ :each | each validate ]
+]
+
 { #category : 'accessing' }
 OPDiagramController >> view [
 
diff --git a/repository/OpenPonk-Core/OPElementController.class.st b/repository/OpenPonk-Core/OPElementController.class.st
index 1a41a6d1..49d439c7 100644
--- a/repository/OpenPonk-Core/OPElementController.class.st
+++ b/repository/OpenPonk-Core/OPElementController.class.st
@@ -215,6 +215,7 @@ OPElementController >> renderFigureIn: aCanvas [
 { #category : 'construction' }
 OPElementController >> showWithoutDependentInDiagram: aDiagramController [
 
+	self validate.
 	self ensureShownDependenciesInDiagram: aDiagramController.
 	aDiagramController addController: self.
 	self ensureDiagramElement.
diff --git a/repository/OpenPonk-Core/OPModelInvalid.class.st b/repository/OpenPonk-Core/OPModelInvalid.class.st
new file mode 100644
index 00000000..b1f8c955
--- /dev/null
+++ b/repository/OpenPonk-Core/OPModelInvalid.class.st
@@ -0,0 +1,7 @@
+Class {
+	#name : 'OPModelInvalid',
+	#superclass : 'Warning',
+	#category : 'OpenPonk-Core-Controllers',
+	#package : 'OpenPonk-Core',
+	#tag : 'Controllers'
+}
diff --git a/repository/OpenPonk-Core/OPProjectController.class.st b/repository/OpenPonk-Core/OPProjectController.class.st
index cd35edfa..132dda1d 100644
--- a/repository/OpenPonk-Core/OPProjectController.class.st
+++ b/repository/OpenPonk-Core/OPProjectController.class.st
@@ -395,15 +395,16 @@ OPProjectController >> selectInDiagram: aModelElement [
 OPProjectController >> updateDiagram: aDiagram [
 
 	| focusedController |
-	focusedController := workbench focusedEditor ifNotNil: [ :editor | 
+	controllers do: [ :each | each validate ].
+	focusedController := workbench focusedEditor ifNotNil: [ :editor |
 		                     editor diagramController ].
 	controllers
 		detect: [ :ctrl | ctrl diagramElement = aDiagram ]
-		ifFound: [ :ctrl | 
+		ifFound: [ :ctrl |
 			aDiagram isOpen: true.
 			aDiagram isRendered ifTrue: [ aDiagram updateFromRender ].
 			aDiagram isSelected: ctrl = focusedController ]
-		ifNone: [ 
+		ifNone: [
 			aDiagram
 				isOpen: false;
 				isSelected: false ]
diff --git a/repository/OpenPonk-Core/OPShape.class.st b/repository/OpenPonk-Core/OPShape.class.st
index dab3b030..6da8dbac 100644
--- a/repository/OpenPonk-Core/OPShape.class.st
+++ b/repository/OpenPonk-Core/OPShape.class.st
@@ -271,6 +271,8 @@ OPShape >> modelElement [
 OPShape >> modelElement: anObject [
 
 	anObject ifNil: [ ^ self modelElements: #(  ) ].
+	(self modelElements size = 1 and: [
+		 self modelElements first == anObject ]) ifTrue: [ ^ self ].
 	self modelElements: { anObject }
 ]
 
@@ -319,6 +321,7 @@ OPShape >> ownedElement: aShape renderedIn: aCanvas [
 
 { #category : 'accessing' }
 OPShape >> ownedElements [
+
 	^ ownedElements
 ]
 
diff --git a/repository/OpenPonk-Spec/OPEditor.class.st b/repository/OpenPonk-Spec/OPEditor.class.st
index 0656ed0f..f12e4f06 100644
--- a/repository/OpenPonk-Spec/OPEditor.class.st
+++ b/repository/OpenPonk-Spec/OPEditor.class.st
@@ -262,7 +262,7 @@ OPEditor >> setModelBeforeInitialization: aPlugin [
 ]
 
 { #category : 'updating' }
-OPEditor >> tabDeleted [
+OPEditor >> tabClosed [
 
 	self workbench projectController updateDiagram:
 		diagramController diagramElement.
@@ -271,6 +271,17 @@ OPEditor >> tabDeleted [
 	diagramController removeRender
 ]
 
+{ #category : 'updating' }
+OPEditor >> tabClosedWhileClosingWorkbench: discardingChanges [
+
+	discardingChanges ifTrue: [ ^ self ].
+	self workbench projectController updateDiagram:
+		diagramController diagramElement.
+	self workbench projectController removeDiagramController:
+		diagramController.
+	diagramController removeRender
+]
+
 { #category : 'updating' }
 OPEditor >> updateUndoRedo [
 	self flag: #unused.
diff --git a/repository/OpenPonk-Spec/OPWorkbench.class.st b/repository/OpenPonk-Spec/OPWorkbench.class.st
index d162cb57..fae14d0c 100644
--- a/repository/OpenPonk-Spec/OPWorkbench.class.st
+++ b/repository/OpenPonk-Spec/OPWorkbench.class.st
@@ -126,19 +126,22 @@ OPWorkbench >> closeEditorOfDiagram: aDiagram [
 { #category : 'opening' }
 OPWorkbench >> closedTabOfEditor: anEditor [
 
-	self projectController updateDiagram:
-		anEditor diagramController diagramElement.
-	anEditor tabDeleted.
-	topToolbar activeEditor: nil.
-	editors removeKey: anEditor diagramController diagramElement.
-	anEditor diagramController diagramElement isSelected: false.
-	focusedEditor = anEditor ifTrue: [ 
+	self closedTabOfEditor: anEditor whileClosingWorkbench: false
+]
+
+{ #category : 'opening' }
+OPWorkbench >> closedTabOfEditor: anEditor whileClosingWorkbench: discardChanges [
+
+	focusedEditor = anEditor ifTrue: [
 		focusedEditor := nil.
 		self announce: (OPEditorUnfocused on: anEditor) ].
+	anEditor tabClosedWhileClosingWorkbench: discardChanges.
+	topToolbar activeEditor: nil.
+	editors removeKey: anEditor diagramController diagramElement.
 	self announce: (OPEditorClosed on: anEditor)
 ]
 
-{ #category : 'as yet unclassified' }
+{ #category : 'initialization' }
 OPWorkbench >> connectPresenters [
 
 	super connectPresenters.
@@ -197,7 +200,7 @@ OPWorkbench >> initialize [
 	super initialize
 ]
 
-{ #category : 'as yet unclassified' }
+{ #category : 'initialization' }
 OPWorkbench >> initializePresenters [
 
 	topToolbar := self instantiate: OPWorkbenchToolbar.
@@ -211,7 +214,7 @@ OPWorkbench >> initializePresenters [
 		add: notebook
 ]
 
-{ #category : 'as yet unclassified' }
+{ #category : 'initialization' }
 OPWorkbench >> initializeWindow: aWindow [
 
 	aWindow
@@ -220,7 +223,9 @@ OPWorkbench >> initializeWindow: aWindow [
 		initialExtent: self class initialExtent;
 		whenClosedDo: [
 			editors valuesDo: [ :each |
-					self closedTabOfEditor: (each at: #editor) ] ]
+					self
+						closedTabOfEditor: (each at: #editor)
+						whileClosingWorkbench: true ] ]
 ]
 
 { #category : 'accessing - spec' }
@@ -284,7 +289,7 @@ OPWorkbench >> openProject: aProject [
 	self updateTitle.
 ]
 
-{ #category : 'as yet unclassified' }
+{ #category : 'opening' }
 OPWorkbench >> pageRemoved: aPage [
 
 	"activePresenter is editor"
@@ -307,7 +312,7 @@ OPWorkbench >> projectTree [
 	^ projectTree
 ]
 
-{ #category : 'as yet unclassified' }
+{ #category : 'opening' }
 OPWorkbench >> showAllElementsInAllDiagrams [
 
 	self projectController controllers do: [ :each |