diff --git a/src/Grafoscopio/GrafoscopioNode.class.st b/src/Grafoscopio/GrafoscopioNode.class.st
index 1c6c178..28ef407 100644
--- a/src/Grafoscopio/GrafoscopioNode.class.st
+++ b/src/Grafoscopio/GrafoscopioNode.class.st
@@ -13,8 +13,13 @@ Class {
 	#superclass : #Object,
 	#instVars : [
 		'header',
+		'created',
+		'edited',
 		'headers',
 		'key',
+		'id',
+		'selected',
+		'expanded',
 		'icon',
 		'body',
 		'tags',
@@ -102,7 +107,10 @@ GrafoscopioNode >> addNode: aNode [
 GrafoscopioNode >> addNodeAfterMe [
 	"Adds a generic node after the given node so they become slibings of the same parent"
 	| genericNode |
-	genericNode := self class new header: 'newNode'; body: ''.
+	genericNode := self class new 
+		created: DateAndTime now printString;
+		header: 'newNode'; 
+		body: ''.
 	self parent children add: genericNode after: self.
 	genericNode parent: self parent.
 	genericNode level: self level.
@@ -182,6 +190,17 @@ GrafoscopioNode >> asSton [
 	"Exports current tree as STON format"
 	| stonOutput |
 	
+	stonOutput := '' writeStream.
+	stonOutput nextPutAll:  (STON toStringPretty: self "flatten").	
+	^stonOutput contents 
+	
+]
+
+{ #category : #exporting }
+GrafoscopioNode >> asStonFromRoot [
+	"Exports current tree as STON format"
+	| stonOutput |
+	
 	stonOutput := '' writeStream.
 	self flatten.
 	stonOutput nextPutAll:  (STON toStringPretty: self children).	
@@ -198,24 +217,29 @@ GrafoscopioNode >> asText [
 GrafoscopioNode >> becomeDefaultTestTree [
 	| node1 node2 node3 node4 |
 	self 
-		level: 0; 
+		created: DateAndTime now printString;
+		level: 0;
 		header: 'Arbol principal'.	
 	node1 := self class new
+		created: DateAndTime now printString;
 		header: 'Markup';
 		body:  'I am <b>just a node with markup</b>';
 		tagAs: 'text';
 		links: 'temp.md';
 		level: 1.
 	node2 := self class new
+		created: DateAndTime now printString;
 		header: '%output Code';
 		tagAs: 'código';
 		body:  '(ConfigurationOfGrafoscopio>>#version14:) sourceCode'.
 	node3 := self class new
+		created: DateAndTime now printString;
 		header: '%invisible';
 		tagAs: 'text';
 		body:  '<i>Just testing</i>'.
 	node1 addNode: node3.
 	node4 := self class new
+		created: DateAndTime now printString;
 		header: 'Something';
 		tagAs: 'text';
 		body:  '<h1>else</h1>'.
@@ -231,10 +255,12 @@ GrafoscopioNode >> becomeDefaultTree [
 	| node1 |
 	self class new.
 	self
+		created: DateAndTime now printString;
 		level: 0;
 		header: 'Arbol principal';
 		tagAs: 'código'.	
 	node1 := self class new
+		created: DateAndTime now printString;
 		header: 'Node 1';
 		body:  '';
 		tagAs: 'text'.	
@@ -252,8 +278,6 @@ GrafoscopioNode >> body [
 
 { #category : #accessing }
 GrafoscopioNode >> body: anObject [
-	"Sets the receivers body to the given object"
-	
 	body := anObject
 ]
 
@@ -278,9 +302,26 @@ GrafoscopioNode >> bodyAsMarkdownInto: aStream [
 
 { #category : #operation }
 GrafoscopioNode >> checksum [
+	"I return the SHA1SUM of the current node. 
+	I'm used to test changes on the node contents, without including changes in the children."
+	| nodeCopy |
+	nodeCopy := self surfaceCopy.
+	^ self checksumFor: nodeCopy asSton.
+]
+
+{ #category : #utility }
+GrafoscopioNode >> checksumFor: aText [
 	"I return the SHA1SUM of the current tree. I'm used to test changes on the contents
 	and for traceability of how the document tree is converted to other formats, as markdown."
-	^ (SHA1 new hashMessage: self root flatten asSton) hex
+	^ (SHA1 new hashMessage: aText) hex
+]
+
+{ #category : #operation }
+GrafoscopioNode >> checksumForRootSubtree [
+	"I return the SHA1SUM of the current tree. I'm used to test changes on the contents
+	and for traceability of how the document tree is converted to other formats, as markdown."
+	^ self checksumFor: self root flatten asStonFromRoot.
+	"^ (SHA1 new hashMessage: self root flatten asStonFromRoot) hex"
 ]
 
 { #category : #accessing }
@@ -302,7 +343,7 @@ GrafoscopioNode >> children: aCollection [
 GrafoscopioNode >> content [
 	"Returns the receivers body"
 	
-	^ body
+	^ self body
 
 ]
 
@@ -320,6 +361,19 @@ GrafoscopioNode >> copyToClipboard [
 	
 ]
 
+{ #category : #accessing }
+GrafoscopioNode >> created [
+	
+	^ created
+]
+
+{ #category : #accessing }
+GrafoscopioNode >> created: aTimestamp [
+	"I tell when this object was created"
+	
+	created :=  aTimestamp
+]
+
 { #category : #operation }
 GrafoscopioNode >> currentLink [
 	"TODO: This method should not only select sanitized links, but also provide ways to detect wich link
@@ -350,6 +404,34 @@ GrafoscopioNode >> demote [
 	
 ]
 
+{ #category : #'as yet unclassified' }
+GrafoscopioNode >> detectSelectionIndex [
+	"I tell which is the index of the current selected node or return the first childre
+	(indexed at 1) if is not found."
+
+	| root |
+	root := self root.
+	root preorderTraversal allButFirst doWithIndex: [ :currentNode :index |
+		currentNode isSelected ifTrue: [ ^ index ] ].
+	^ 1.
+]
+
+{ #category : #accessing }
+GrafoscopioNode >> edited [
+	^ edited
+]
+
+{ #category : #accessing }
+GrafoscopioNode >> edited: aTimestamp [
+	"I store the last time when a node was edited.	
+	Because nodes in the notebook have a autosave feature, I'm updated automatically when nodes are
+	edited from the GUI.
+	
+	If I'm in the notebook root (i.e. node's level equals 0) I should store the last time the notebook
+	was saved on the hard drive."
+	edited := aTimestamp
+]
+
 { #category : #'custom markup' }
 GrafoscopioNode >> embedAll [
 	"This is just a previous part of the messy markDownContent. The %embed-all keyword should be revaluated.
@@ -384,6 +466,13 @@ GrafoscopioNode >> embeddedNodes [
 	^ self children select: [:each | each headerStartsWith: '%embed']
 ]
 
+{ #category : #accessing }
+GrafoscopioNode >> expanded: aBoolean [
+	"I tell if the node is expanded from the UI, showing my children.
+	Several nodes can be expanded in a single document."
+	selected := aBoolean 
+]
+
 { #category : #exporting }
 GrafoscopioNode >> exportCodeBlockTo: aStream [
 	"I convert the content of a node taged as 'código' (code) as pandoc markdown and put it 
@@ -564,6 +653,18 @@ GrafoscopioNode >> icon: aSymbol [
 	icon := aSymbol
 ]
 
+{ #category : #accessing }
+GrafoscopioNode >> id [
+	^id
+]
+
+{ #category : #accessing }
+GrafoscopioNode >> id: aChecksum [
+	"I'm a unique identifier that changes when node content changes (i.e. header, body, links)."	
+		
+	id := aChecksum  
+]
+
 { #category : #importing }
 GrafoscopioNode >> importHtmlLink [
 	"I take the last link and import its contents in node body. "
@@ -607,6 +708,21 @@ GrafoscopioNode >> isEmpty [
 	body ifNil: [ ^ true ] ifNotNil: [ ^ false ] 
 ]
 
+{ #category : #operation }
+GrafoscopioNode >> isSavedAfterLastEdition [
+	| root  |
+	root := self root.
+	root edited ifNil: [ ^ false ].
+	^ self unsavedNodes isEmpty.
+	"self unsavedNodes isEmpty ifFalse: [ ^ self unsavedNodes inspect ]"
+]
+
+{ #category : #testing }
+GrafoscopioNode >> isSelected [
+	self selected ifNil: [ ^ false ].
+	^ self selected. 
+]
+
 { #category : #operation }
 GrafoscopioNode >> isTaggedAs: aString [
 	self tags ifEmpty: [ self tagAs: 'text' ].
@@ -688,12 +804,12 @@ GrafoscopioNode >> links: anObject [
 ]
 
 { #category : #operation }
-GrafoscopioNode >> linksToMarkdownFile [
+GrafoscopioNode >> linksToMarkupFile [
 	"I detect if the links contains any reference to a file ending in '.md' or '.markdown'"
 	self links 
 		ifNotNil: [ 
 			self links 
-				detect: [:l | (l endsWith: '.md') or: [ l endsWith: '.markdown']]
+				detect: [:l | (l endsWithAnyOf:  #('.md' '.markdown' '.md.html'))]
 					ifFound: [ ^ true ]
 					ifNone: [^ false]].
 	^ false
@@ -901,6 +1017,21 @@ GrafoscopioNode >> preorderTraversal [
 	^ nodesInPreorder.
 ]
 
+{ #category : #'as yet unclassified' }
+GrafoscopioNode >> preorderTraversalIndex [
+	"I tell which place I occupy in the tree children (without counting the root)."
+
+	| root |
+	root := self root.
+	root preorderTraversalRootChildren doWithIndex: [ :currentNode :index |
+		currentNode = self ifTrue: [^ index] ].
+]
+
+{ #category : #'as yet unclassified' }
+GrafoscopioNode >> preorderTraversalRootChildren [
+	^ self root preorderTraversal allButFirst
+]
+
 { #category : #movement }
 GrafoscopioNode >> promote [
 	"Moves the current node up in the hierachy, making it a slibing of its current parent"
@@ -991,8 +1122,20 @@ GrafoscopioNode >> saveContent: anObject [
 ]
 
 { #category : #operation }
-GrafoscopioNode >> selectMarkdownSubtreesToExport [
-	^ (self root preorderTraversal) select: [ :each | each linksToMarkdownFile ].
+GrafoscopioNode >> selectMarkupSubtreesToExport [
+	^ (self root preorderTraversal) select: [ :each | each linksToMarkupFile ].
+]
+
+{ #category : #accessing }
+GrafoscopioNode >> selected [
+	^ selected 
+]
+
+{ #category : #accessing }
+GrafoscopioNode >> selected: aBoolean [
+	"I tell if the node is selected from the UI.
+	Once other node is selected my value becomes false."
+	selected := aBoolean 
 ]
 
 { #category : #accessing }
@@ -1024,10 +1167,13 @@ GrafoscopioNode >> surfaceCopy [
 	to the rest of the container tree, which could end in copying the whole tree."
 	| newNode |
 	newNode := self class new.
-	^ newNode
+	newNode
 		header: self header;
 		body: self body;
-		tags: self tags.
+		tags: self tags;
+		level: self level.
+	self links ifNotEmpty: [ newNode links addAll: self links ].
+	^ newNode.
 	
 	
 ]
@@ -1083,6 +1229,36 @@ GrafoscopioNode >> toggleCodeText [
 		ifTrue: [ ^ self tags replaceAll: 'código' with: 'text' ].
 ]
 
+{ #category : #accessing }
+GrafoscopioNode >> toggleSelected [
+	"I made the receiver the current selected node and deselect all other nodes."
+	
+	| root previousSelection |	
+	self isSelected ifTrue: [ ^ self ].
+	root := self root.
+	previousSelection := self preorderTraversalRootChildren at: (self detectSelectionIndex).
+	previousSelection selected: false.
+	self selected: true.
+	^ self.
+]
+
+{ #category : #operation }
+GrafoscopioNode >> unsavedNodes [
+	"I collect all nodes that have changed after the last saving"
+	| lastSavedOn root unsavedNodes |
+	root := self root.
+	lastSavedOn := root edited asDateAndTime.
+	unsavedNodes := root preorderTraversal select: [ :currentNode | 
+		currentNode edited isNotNil and: [currentNode edited asDateAndTime > lastSavedOn] ].
+	^ unsavedNodes.
+
+]
+
+{ #category : #'as yet unclassified' }
+GrafoscopioNode >> updateEditionTimestamp [
+	self edited: DateAndTime now printString 
+]
+
 { #category : #importing }
 GrafoscopioNode >> uploadBodyFrom: fileLocator filteredFor: selectedLink [
 	(self linksFilters contains: selectedLink)
diff --git a/src/Grafoscopio/GrafoscopioNodeTest.class.st b/src/Grafoscopio/GrafoscopioNodeTest.class.st
index f86983c..7c6ff65 100644
--- a/src/Grafoscopio/GrafoscopioNodeTest.class.st
+++ b/src/Grafoscopio/GrafoscopioNodeTest.class.st
@@ -60,7 +60,7 @@ GrafoscopioNodeTest >> testHasMarkdownSubtreesToExport [
 	Please see look #becomeDefaultTestTree message to see the details that makes this test true."
 	| tree | 
 	tree := GrafoscopioNode new becomeDefaultTestTree.
-	self assert: tree selectMarkdownSubtreesToExport isNotEmpty equals: true.
+	self assert: tree selectMarkupSubtreesToExport isNotEmpty equals: true.
 	
 ]
 
@@ -69,6 +69,17 @@ GrafoscopioNodeTest >> testInitializeIsOk [
 	self shouldnt: [ GrafoscopioNode new ] raise: Error 
 ]
 
+{ #category : #tests }
+GrafoscopioNodeTest >> testNodeSelection [
+	| tree child1 | 
+	tree := GrafoscopioNode new becomeDefaultTestTree.
+	child1 := tree preorderTraversalRootChildren at: 1.
+	child1 selected: true.
+	self assert: tree detectSelectionIndex equals: 1
+	
+	
+]
+
 { #category : #tests }
 GrafoscopioNodeTest >> testPromoteNode [
 	| tree child1 child2 | 
@@ -135,3 +146,16 @@ GrafoscopioNodeTest >> testSanitizedLink [
 	self assert: (node sanitizeDefaultLink = 'https://docutopia.tupale.co/hackbo:hackbot')   equals: true
 
 ]
+
+{ #category : #tests }
+GrafoscopioNodeTest >> testToggleNodeSelection [
+	"I verify that a selected node can be unchosen once a new selection has been done."
+
+	| tree testNode1 testNode2 |
+	tree := GrafoscopioNode new becomeDefaultTestTree.
+	testNode1 := (tree preorderTraversalRootChildren at: 1) selected: true.
+	self assert: tree detectSelectionIndex equals: testNode1 preorderTraversalIndex.
+	testNode2 := (tree preorderTraversalRootChildren at: 2).
+	testNode2 toggleSelected.
+	self assert: tree detectSelectionIndex equals: testNode2 preorderTraversalIndex
+]
diff --git a/src/Grafoscopio/GrafoscopioNotebook.class.st b/src/Grafoscopio/GrafoscopioNotebook.class.st
index d0e38b3..de3f647 100644
--- a/src/Grafoscopio/GrafoscopioNotebook.class.st
+++ b/src/Grafoscopio/GrafoscopioNotebook.class.st
@@ -72,17 +72,41 @@ GrafoscopioNotebook >> addNode [
 	self notebookContent: notebook.
 ]
 
+{ #category : #persistence }
+GrafoscopioNotebook >> askToSaveBeforeClosing [
+
+	| saveChanges |
+	
+	saveChanges := UIManager default
+	question: 'Do you want to save changes in the notebook before closing?' 
+	title:  'Save changes before closing?'.
+	saveChanges ifNil: [ ^ self notebook unsavedNodes inspect ].
+	^ saveChanges
+]
+
 { #category : #operation }
 GrafoscopioNotebook >> autoSaveBodyOf: aNode [
-	| playground |
-	self body class = GrafoscopioTextModel  
-		ifTrue: [ body body whenTextChanged: [ :arg | aNode body: arg ] ].
-	body body class = GlamourPresentationModel
+	| playground bodyContents |
+	bodyContents := aNode body.
+	self body class = GrafoscopioTextModel 
+		ifTrue: [ self body body whenTextChanged: [ :arg | 
+				aNode body: arg.
+				"self body body whenTextIsAccepted: [:bodyText | 
+					self inform: bodyText.
+					aNode updateEditionTimestamp ]."
+				bodyContents = arg ifFalse: [ 
+					"self inform: arg."
+					"aNode updateEditionTimestamp" ]]].
+	self body body class = GlamourPresentationModel
 		ifFalse: [ ^ self ].
-	playground := body body glmPres.
+	playground := self body body glmPres.
 	playground
 		onChangeOfPort: #text
-		act: [ :x | aNode body: (x pane port: #entity) value content ]
+		act: [ :x | 
+			aNode body: (x pane port: #entity) value content.
+			"aNode updateEditionTimestamp."
+			"self inform: aNode edited" ]
+		
 ]
 
 { #category : #accessing }
@@ -96,7 +120,7 @@ GrafoscopioNotebook >> body: anObject [
 ]
 
 { #category : #utilities }
-GrafoscopioNotebook >> checksum [
+GrafoscopioNotebook >> checksumForRootSubtree [
 	"I return the checksum (crypto hash) of the workingFile where this notebook is being stored.
 	I'm useful for data provenance and traceability of derivated files coming from this source
 	notebook."
@@ -187,9 +211,9 @@ GrafoscopioNotebook >> downloadImages [
 ]
 
 { #category : #persistence }
-GrafoscopioNotebook >> exportAllSubtreesAsMarkdow [
+GrafoscopioNotebook >> exportAllSubtreesAsMarkup [
 	| toBeExported |
-	toBeExported := self notebook selectMarkdownSubtreesToExport.
+	toBeExported := self notebook selectMarkupSubtreesToExport.
 	toBeExported ifEmpty: [ ^ self ].
 	toBeExported do: [ :each | self subtreeAsMarkdownFileFor: each ].
 	self inform: toBeExported size asString , ' exported markdown subtrees.'
@@ -262,11 +286,13 @@ GrafoscopioNotebook >> exportAsPDF [
 { #category : #persistence }
 GrafoscopioNotebook >> exportAsSton: aNotebook on: aFileStream [
 	aNotebook flatten.
-    (STON writer on: aFileStream)
+	self notebook root updateEditionTimestamp.
+   (STON writer on: aFileStream)
 		newLine: String crlf;	
       	prettyPrint: true;
 		keepNewLines: true;
-      	nextPut: aNotebook children
+      	nextPut: aNotebook children.
+	
 ]
 
 { #category : #utility }
@@ -284,7 +310,7 @@ GrafoscopioNotebook >> exportNode: aGrafoscopioNode asMarkdownIn: aFile [
 			stream 
 				nextPutAll: 
 					('---', String cr,
-					'exportedFrom: ', self checksum, String cr) withInternetLineEndings.
+					'exportedFrom: ', self checksumForRootSubtree, String cr) withInternetLineEndings.
 			aGrafoscopioNode metadataAsYamlIn: stream.
 			stream 
 				nextPutAll: 
@@ -313,6 +339,11 @@ GrafoscopioNotebook >> findAndReplace [
 	
 ]
 
+{ #category : #testing }
+GrafoscopioNotebook >> hasAWorkingFileDefined [
+	self workingFile ifNil: [ ^ false ] ifNotNil: [ ^ true ]
+]
+
 { #category : #accessing }
 GrafoscopioNotebook >> header [
 	^ header
@@ -394,8 +425,12 @@ GrafoscopioNotebook >> initializePresenter [
 		(tree highlightedItem content header) = arg
 			ifFalse: [ 
 				tree highlightedItem content header: arg.
+				tree highlightedItem content updateEditionTimestamp.
 				tree roots: tree roots]].
-	links whenTextChanged: [ :arg | tree highlightedItem content addLink: arg ]
+	links whenTextChanged: [ :arg | 
+		tree highlightedItem content addLink: arg.
+		tree highlightedItem content updateEditionTimestamp. 
+		 ]
 ]
 
 { #category : #initialization }
@@ -404,6 +439,7 @@ GrafoscopioNotebook >> initializeWidgets [
 	header := self newTextInput.
 	header autoAccept: true.
 	body := self newText.
+	body class logCr.
 	body disable.
 	body text: '<- Select a node'.
 	body autoAccept: true.
@@ -420,6 +456,17 @@ GrafoscopioNotebook >> initializeWidgets [
 	self askOkToClose: true.
 ]
 
+{ #category : #persistence }
+GrafoscopioNotebook >> isSaved [
+	"I tell if a notebook has been saved in a persistence storage, including last editions."
+	^ self hasAWorkingFileDefined and: [self isSavedAfterLastEdition ].
+]
+
+{ #category : #testing }
+GrafoscopioNotebook >> isSavedAfterLastEdition [
+	^ self notebook isSavedAfterLastEdition
+]
+
 { #category : #accessing }
 GrafoscopioNotebook >> links [
 	^ links
@@ -630,9 +677,10 @@ GrafoscopioNotebook >> notebookSubMenu [
 						action: [ self defineDebugMessageUI ] ] ]
 ]
 
-{ #category : #private }
+{ #category : #'event handling' }
 GrafoscopioNotebook >> okToChange [
-	^ true
+	
+	self isSaved ifTrue: [ ^ true ] ifFalse: [ ^ self askToSaveBeforeClosing ]
 ]
 
 { #category : #persistence }
@@ -799,7 +847,7 @@ GrafoscopioNotebook >> removeNode [
 
 { #category : #persistence }
 GrafoscopioNotebook >> saveToFile: aFileReference [
-	"I save the current tree/document to a file."
+	"I save the current tree/document to a file and update storage timestamp."
 
 	aFileReference ifNil: [ self inform: 'No file selected for saving. Save NOT done.'. ^ self ].
 	workingFile := aFileReference.
@@ -831,6 +879,7 @@ GrafoscopioNotebook >> saveWorkingNotebook [
 	self workingFile 
 		ifNil: [ self saveToFileUI ] 
 		ifNotNil: [ self saveToFile: workingFile ].
+	self notebook root updateEditionTimestamp.	
 	GfUIHelpers updateRecentNotebooksWith: workingFile
 	
 	
@@ -891,7 +940,7 @@ GrafoscopioNotebook >> topBar [
 						name: nil;
 						description: 'Export all Markdown subtrees';
 						icon: (self iconNamed: #glamorousMore);
-						action: [ self exportAllSubtreesAsMarkdow ] ].
+						action: [ self exportAllSubtreesAsMarkup ] ].
 			group
 				addItem: [ :item | 
 					item
@@ -1062,6 +1111,7 @@ GrafoscopioNotebook >> updateBodyFor: aNodeContainer [
 	tree needRebuild: false.
 	body needRebuild: true.
 	aNode := aNodeContainer content.
+	aNode toggleSelected.
 	header text: aNode header.
 	body := self instantiate: aNode specModelClass new.
 	body content: aNode body.
diff --git a/src/Grafoscopio/GrafoscopioTextModel.class.st b/src/Grafoscopio/GrafoscopioTextModel.class.st
index e9dc19a..6bcd3f8 100644
--- a/src/Grafoscopio/GrafoscopioTextModel.class.st
+++ b/src/Grafoscopio/GrafoscopioTextModel.class.st
@@ -4,7 +4,7 @@ Usually my content is markdown text.
 "
 Class {
 	#name : #GrafoscopioTextModel,
-	#superclass : #ComposableModel,
+	#superclass : #ComposablePresenter,
 	#instVars : [
 		'body'
 	],