diff --git a/sources/bordertitleblock.cpp b/sources/bordertitleblock.cpp
index 17378b89b..56725c280 100644
--- a/sources/bordertitleblock.cpp
+++ b/sources/bordertitleblock.cpp
@@ -55,11 +55,8 @@ BorderTitleBlock::BorderTitleBlock(QObject *parent) :
 	m_titleblock_template_renderer = new TitleBlockTemplateRenderer(this);
 	m_titleblock_template_renderer -> setTitleBlockTemplate(QETApp::defaultTitleBlockTemplate());
 
-	// disable the QPicture-based cache from Qt 4.8 to avoid rendering errors and crashes
-#if QT_VERSION < QT_VERSION_CHECK(4, 8, 0)	// ### Qt 6: remove
-#else
+	// disable the QPicture-based cache to avoid rendering errors and crashes
 	m_titleblock_template_renderer -> setUseCache(false);
-#endif
 
 	// dimensions par defaut du schema
 	importBorder(BorderProperties());
@@ -239,7 +236,8 @@ void BorderTitleBlock::borderToXml(QDomElement &xml_elmt) {
 	xml_elmt.setAttribute("displayrows", rowsAreDisplayed() ? "true" : "false");
 
 	// attribut datant de la version 0.1 - laisse pour retrocompatibilite
-	xml_elmt.setAttribute("height", QString("%1").arg(diagramHeight()));
+	// attribute from version 0.1 - leave for backwards-compatibility
+	xml_elmt.setAttribute("height",      QString("%1").arg(diagramHeight()));
 }
 
 /**
@@ -946,10 +944,10 @@ QString BorderTitleBlock::incrementLetters(const QString &string) {
 		if (last_digit != 'Z') {
 			// increments the last digit
 			// incremente le dernier digit
-		last_digit = (char)(string[string.length()-1].unicode()) + 1;
+			last_digit = (char)(string[string.length()-1].unicode()) + 1;
 			return(first_digits + QString(last_digit));
 		} else {
-			return(incrementLetters(first_digits) + "A");
+			return(incrementLetters(first_digits) % "A");
 		}
 	}
 }
diff --git a/sources/conductornumexport.cpp b/sources/conductornumexport.cpp
index a18bf527b..880fbb988 100644
--- a/sources/conductornumexport.cpp
+++ b/sources/conductornumexport.cpp
@@ -72,14 +72,7 @@ bool ConductorNumExport::toCsv()
 		if (file.open(QIODevice::WriteOnly | QIODevice::Text))
 		{
 			QTextStream stream(&file);
-#if QT_VERSION < QT_VERSION_CHECK(5, 15, 0)	// ### Qt 6: remove
-			stream << wiresNum() << endl;
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 5.15 or later")
-#endif
 			stream << wiresNum() << &Qt::endl(stream);
-#endif
 		}
 		else {
 			return false;
diff --git a/sources/conductorproperties.cpp b/sources/conductorproperties.cpp
index 88571ce0c..eaa8080fe 100644
--- a/sources/conductorproperties.cpp
+++ b/sources/conductorproperties.cpp
@@ -376,31 +376,31 @@ void ConductorProperties::fromXml(QDomElement &e)
 */
 void ConductorProperties::toSettings(QSettings &settings, const QString &prefix) const
 {
-	settings.setValue(prefix + "color", color.name());
-	settings.setValue(prefix + "bicolor", m_bicolor);
-	settings.setValue(prefix + "color2", m_color_2.name());
-	settings.setValue(prefix + "dash-size", m_dash_size);
-	settings.setValue(prefix + "style", writeStyle());
-	settings.setValue(prefix + "type", typeToString(type));
-	settings.setValue(prefix + "text", text);
-	settings.setValue(prefix + "text_color", text_color.name());
-	settings.setValue(prefix + "formula", m_formula);
-	settings.setValue(prefix + "cable", m_cable);
-	settings.setValue(prefix + "bus", m_bus);
-	settings.setValue(prefix + "function", m_function);
-	settings.setValue(prefix + "tension_protocol", m_tension_protocol);
-	settings.setValue(prefix + "conductor_color", m_wire_color);
-	settings.setValue(prefix + "conductor_section", m_wire_section);
-	settings.setValue(prefix + "textsize", QString::number(text_size));
-	settings.setValue(prefix + "size", QString::number(cond_size));
-	settings.setValue(prefix + "displaytext", m_show_text);
-	settings.setValue(prefix + "onetextperfolio", m_one_text_per_folio);
-	settings.setValue(prefix + "vertirotatetext", QString::number(verti_rotate_text));
-	settings.setValue(prefix + "horizrotatetext", QString::number(horiz_rotate_text));
+	settings.setValue(prefix % "color", color.name());
+	settings.setValue(prefix % "bicolor", m_bicolor);
+	settings.setValue(prefix % "color2", m_color_2.name());
+	settings.setValue(prefix % "dash-size", m_dash_size);
+	settings.setValue(prefix % "style", writeStyle());
+	settings.setValue(prefix % "type", typeToString(type));
+	settings.setValue(prefix % "text", text);
+	settings.setValue(prefix % "text_color", text_color.name());
+	settings.setValue(prefix % "formula", m_formula);
+	settings.setValue(prefix % "cable", m_cable);
+	settings.setValue(prefix % "bus", m_bus);
+	settings.setValue(prefix % "function", m_function);
+	settings.setValue(prefix % "tension_protocol", m_tension_protocol);
+	settings.setValue(prefix % "conductor_color", m_wire_color);
+	settings.setValue(prefix % "conductor_section", m_wire_section);
+	settings.setValue(prefix % "textsize", QString::number(text_size));
+	settings.setValue(prefix % "size", QString::number(cond_size));
+	settings.setValue(prefix % "displaytext", m_show_text);
+	settings.setValue(prefix % "onetextperfolio", m_one_text_per_folio);
+	settings.setValue(prefix % "vertirotatetext", QString::number(verti_rotate_text));
+	settings.setValue(prefix % "horizrotatetext", QString::number(horiz_rotate_text));
 
 	QMetaEnum me = QMetaEnum::fromType<Qt::Alignment>();
-	settings.setValue(prefix + "horizontal-alignment", me.valueToKey(m_horizontal_alignment));
-	settings.setValue(prefix + "vertical-alignment", me.valueToKey(m_vertical_alignment));
+	settings.setValue(prefix % "horizontal-alignment", me.valueToKey(m_horizontal_alignment));
+	settings.setValue(prefix % "vertical-alignment", me.valueToKey(m_vertical_alignment));
 
 	singleLineProperties.toSettings(settings, prefix);
 }
@@ -417,36 +417,36 @@ void ConductorProperties::fromSettings(QSettings &settings, const QString &prefi
 	QColor settings_color_2 = QColor(settings.value(prefix + "color2").toString());
 	m_color_2 = (settings_color_2.isValid()? settings_color_2 : QColor(Qt::black));
 
-	m_bicolor   = settings.value(prefix + "bicolor", false).toBool();
-	m_dash_size = settings.value(prefix + "dash-size", 1).toInt();
+	m_bicolor   = settings.value(prefix % "bicolor", false).toBool();
+	m_dash_size = settings.value(prefix % "dash-size", 1).toInt();
 
-	QString setting_type = settings.value(prefix + "type", typeToString(Multi)).toString();
+	QString setting_type = settings.value(prefix % "type", typeToString(Multi)).toString();
 	type = (setting_type == typeToString(Single)? Single : Multi);
 
 	singleLineProperties.fromSettings(settings, prefix);
 
-	text                 = settings.value(prefix + "text", "_").toString();
-	QColor settings_text_color = QColor(settings.value(prefix + "text_color").toString());
+	text                 = settings.value(prefix % "text", "_").toString();
+	QColor settings_text_color = QColor(settings.value(prefix % "text_color").toString());
 	text_color = (settings_text_color.isValid()? settings_text_color : QColor(Qt::black));
-	m_formula            = settings.value(prefix + "formula", "").toString();
-	m_cable              = settings.value(prefix + "cable", "").toString();
-	m_bus                = settings.value(prefix + "bus", "").toString();
-	m_function           = settings.value(prefix + "function", "").toString();
-	m_tension_protocol   = settings.value(prefix + "tension_protocol", "").toString();
-	m_wire_color         = settings.value(prefix + "conductor_color", "").toString();
-	m_wire_section       = settings.value(prefix + "conductor_section", "").toString();
-	text_size            = settings.value(prefix + "textsize", "7").toInt();
-	cond_size            = settings.value(prefix + "size", "1").toInt();
-	m_show_text          = settings.value(prefix + "displaytext", true).toBool();
-	m_one_text_per_folio = settings.value(prefix + "onetextperfolio", false).toBool();
-	verti_rotate_text    = settings.value((prefix + "vertirotatetext"), "270").toDouble();
-	horiz_rotate_text    = settings.value((prefix + "horizrotatetext"), "0").toDouble();
+	m_formula            = settings.value(prefix % "formula", "").toString();
+	m_cable              = settings.value(prefix % "cable", "").toString();
+	m_bus                = settings.value(prefix % "bus", "").toString();
+	m_function           = settings.value(prefix % "function", "").toString();
+	m_tension_protocol   = settings.value(prefix % "tension_protocol", "").toString();
+	m_wire_color         = settings.value(prefix % "conductor_color", "").toString();
+	m_wire_section       = settings.value(prefix % "conductor_section", "").toString();
+	text_size            = settings.value(prefix % "textsize", "7").toInt();
+	cond_size            = settings.value(prefix % "size", "1").toInt();
+	m_show_text          = settings.value(prefix % "displaytext", true).toBool();
+	m_one_text_per_folio = settings.value(prefix % "onetextperfolio", false).toBool();
+	verti_rotate_text    = settings.value((prefix % "vertirotatetext"), "270").toDouble();
+	horiz_rotate_text    = settings.value((prefix % "horizrotatetext"), "0").toDouble();
 
 	QMetaEnum me = QMetaEnum::fromType<Qt::Alignment>();
-	m_horizontal_alignment = Qt::Alignment(me.keyToValue(settings.value(prefix + "horizontal-alignment", "AlignBottom").toString().toStdString().data()));
-	m_vertical_alignment = Qt::Alignment(me.keyToValue(settings.value(prefix + "vertical-alignment", "AlignRight").toString().toStdString().data()));
+	m_horizontal_alignment = Qt::Alignment(me.keyToValue(settings.value(prefix % "horizontal-alignment", "AlignBottom").toString().toStdString().data()));
+	m_vertical_alignment = Qt::Alignment(me.keyToValue(settings.value(prefix % "vertical-alignment", "AlignRight").toString().toStdString().data()));
 
-	readStyle(settings.value(prefix + "style").toString());
+	readStyle(settings.value(prefix % "style").toString());
 }
 
 /**
@@ -811,14 +811,7 @@ void ConductorProperties::readStyle(const QString &style_string) {
 	if (style_string.isEmpty()) return;
 
 	// recupere la liste des couples style / valeur
-#if QT_VERSION < QT_VERSION_CHECK(5, 14, 0)	// ### Qt 6: remove
-	QStringList styles = style_string.split(";", QString::SkipEmptyParts);
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code QString::SkipEmptyParts for QT 5.14 or later")
-#endif
 	QStringList styles = style_string.split(";", Qt::SkipEmptyParts);
-#endif
 
 	QRegularExpression Rx("^(?<name>[a-z-]+): (?<value>[a-z-]+)$");
 	if (!Rx.isValid())
@@ -896,10 +889,10 @@ int SingleLineProperties::operator!=(const SingleLineProperties &other) const
 void SingleLineProperties::toSettings(QSettings &settings,
 				      const QString &prefix) const
 {
-	settings.setValue(prefix + "hasGround",  hasGround);
-	settings.setValue(prefix + "hasNeutral", hasNeutral);
-	settings.setValue(prefix + "phases",     phases);
-	settings.setValue(prefix + "pen",        is_pen);
+	settings.setValue(prefix % "hasGround",  hasGround);
+	settings.setValue(prefix % "hasNeutral", hasNeutral);
+	settings.setValue(prefix % "phases",     phases);
+	settings.setValue(prefix % "pen",        is_pen);
 }
 
 /**
@@ -908,8 +901,8 @@ void SingleLineProperties::toSettings(QSettings &settings,
 */
 void SingleLineProperties::fromSettings(QSettings &settings,
 					const QString &prefix) {
-	hasGround  = settings.value(prefix + "hasGround",  true).toBool();
-	hasNeutral = settings.value(prefix + "hasNeutral", true).toBool();
-	phases     = settings.value(prefix + "phases",     1).toInt();
-	is_pen     = settings.value(prefix + "pen",        false).toBool();
+	hasGround  = settings.value(prefix % "hasGround",  true).toBool();
+	hasNeutral = settings.value(prefix % "hasNeutral", true).toBool();
+	phases     = settings.value(prefix % "phases",     1).toInt();
+	is_pen     = settings.value(prefix % "pen",        false).toBool();
 }
diff --git a/sources/diagram.cpp b/sources/diagram.cpp
index cf966db26..5623c6e93 100644
--- a/sources/diagram.cpp
+++ b/sources/diagram.cpp
@@ -213,8 +213,8 @@ void Diagram::drawBackground(QPainter *p, const QRectF &r) {
 							  .insideBorderRect()
 							  .intersected(r);
 
-		qreal limite_x = rect.x() + rect.width();
-		qreal limite_y = rect.y() + rect.height();
+		qreal limit_x = rect.x() + rect.width();
+		qreal limit_y = rect.y() + rect.height();
 
 		int g_x = (int)ceil(rect.x());
 		while (g_x % xGrid) ++ g_x;
@@ -222,8 +222,8 @@ void Diagram::drawBackground(QPainter *p, const QRectF &r) {
 		while (g_y % yGrid) ++ g_y;
 
 		QPolygon points;
-		for (int gx = g_x ; gx < limite_x ; gx += xGrid) {
-			for (int gy = g_y ; gy < limite_y ; gy += yGrid) {
+		for (int gx = g_x ; gx < limit_x ; gx += xGrid) {
+			for (int gy = g_y ; gy < limit_y ; gy += yGrid) {
 				points << QPoint(gx, gy);
 			}
 		}
@@ -1139,8 +1139,8 @@ Terminal* findTerminal(int conductor_index,
 	assert(conductor_index == 1 || conductor_index == 2);
 
 	auto str_index = QString::number(conductor_index);
-	QString element_index  = QStringLiteral("element")  + str_index;
-	QString terminal_index = QStringLiteral("terminal") + str_index;
+	QString element_index  = QStringLiteral("element")  % str_index;
+	QString terminal_index = QStringLiteral("terminal") % str_index;
 
 	if (f.hasAttribute(element_index)) {
 		QUuid element_uuid = QUuid(f.attribute(element_index));
@@ -1483,14 +1483,6 @@ bool Diagram::fromXml(QDomElement &document,
 	if (content_ptr) {
 		content_ptr -> m_elements           = added_elements;
 		content_ptr -> m_conductors_to_move = added_conductors;
-#if QT_VERSION < QT_VERSION_CHECK(5, 14, 0)	// ### Qt 6: remove
-		content_ptr -> m_text_fields        = added_texts.toSet();
-		content_ptr -> m_images			    = added_images.toSet();
-		content_ptr -> m_shapes			    = added_shapes.toSet();
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 5.14 or later")
-#endif
 		content_ptr -> m_text_fields	= QSet<IndependentTextItem *>(
 					added_texts.begin(),
 					added_texts.end());
@@ -1501,7 +1493,6 @@ bool Diagram::fromXml(QDomElement &document,
 					added_shapes.begin(),
 					added_shapes.end());
 		content_ptr->m_terminal_strip.swap(added_strips);
-#endif
 		content_ptr->m_tables.swap(added_tables);
 	}
 
@@ -1536,9 +1527,9 @@ void Diagram::folioSequentialsFromXml(const QDomElement &root,
 			QStringList list;
 			int i = 1;
 			while (folioseq.hasAttribute(seq
-						     + QString::number(i))) {
+							 % QString::number(i))) {
 				list << folioseq.attribute(
-						seq + QString::number(i));
+						seq % QString::number(i));
 				i++;
 			}
 			hash->insert(title,list);
diff --git a/sources/diagramview.cpp b/sources/diagramview.cpp
index ffe249110..789e4bb86 100644
--- a/sources/diagramview.cpp
+++ b/sources/diagramview.cpp
@@ -93,7 +93,10 @@ DiagramView::DiagramView(Diagram *diagram, QWidget *parent) :
 
 	connect(m_diagram, SIGNAL(showDiagram(Diagram*)), this, SIGNAL(showDiagram(Diagram*)));
 	connect(m_diagram, SIGNAL(sceneRectChanged(QRectF)), this, SLOT(adjustSceneRect()));
-	connect(&(m_diagram -> border_and_titleblock), SIGNAL(diagramTitleChanged(const QString &)), this, SLOT(updateWindowTitle()));
+	// TODO: review the following line. Old line commented out, been broken since commit
+	// "27dcd5ef007a282d1a5a7f2f3dcaefc62669d668".
+	// connect(&(m_diagram -> border_and_titleblock), SIGNAL(diagramTitleChanged(const QString &)), this, SLOT(updateWindowTitle()));
+	connect(&(m_diagram->border_and_titleblock), &BorderTitleBlock::informationChanged, this, &DiagramView::updateWindowTitle);
 	connect(diagram, SIGNAL(findElementRequired(ElementsLocation)), this, SIGNAL(findElementRequired(ElementsLocation)));
 
 	QShortcut *edit_conductor_color_shortcut = new QShortcut(QKeySequence(Qt::Key_F2), this);
@@ -203,18 +206,9 @@ void DiagramView::handleElementDrop(QDropEvent *event)
 		return;
 	}
 
-#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)	// ### Qt 6: remove
-	diagram()->setEventInterface(
-				new DiagramEventAddElement(
-					location, diagram(), mapToScene(event->pos())));
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 	diagram()->setEventInterface(
 				new DiagramEventAddElement(
 					location, diagram(), event->position()));
-#endif
 
 		//Set focus to the view to get event
 	this->setFocus();
@@ -283,17 +277,8 @@ void DiagramView::handleTextDrop(QDropEvent *e) {
 		iti -> setHtml (e -> mimeData() -> text());
 	}
 
-#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)	// ### Qt 6: remove
-
-	m_diagram->undoStack().push(new AddGraphicsObjectCommand(
-									iti, m_diagram, mapToScene(e->pos())));
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 	m_diagram->undoStack().push(new AddGraphicsObjectCommand(
 									iti, m_diagram, e->position()));
-#endif
 }
 
 /**
@@ -447,15 +432,7 @@ void DiagramView::mousePressEvent(QMouseEvent *e)
 
 	if (m_event_interface && m_event_interface->mousePressEvent(e)) return;
 
-		//Start drag view when hold the middle button
-#if QT_VERSION < QT_VERSION_CHECK(5, 15, 1) // ### Qt 6: remove
-	if (e->button() == Qt::MidButton)
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 	if (e->button() == Qt::MiddleButton)
-#endif
 	{
 		m_drag_last_pos = e->pos();
 		viewport()->setCursor(Qt::ClosedHandCursor);
@@ -505,14 +482,7 @@ void DiagramView::mouseMoveEvent(QMouseEvent *e)
 	if (m_event_interface && m_event_interface->mouseMoveEvent(e)) return;
 
 		// Drag the view
-#if QT_VERSION < QT_VERSION_CHECK(5, 15, 1) // ### Qt 6: remove
-	if (e->buttons() == Qt::MidButton)
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 	if (e->buttons() == Qt::MiddleButton)
-#endif
 	{
 		QScrollBar *h = horizontalScrollBar();
 		QScrollBar *v = verticalScrollBar();
@@ -573,14 +543,7 @@ void DiagramView::mouseReleaseEvent(QMouseEvent *e)
 	if (m_event_interface && m_event_interface->mouseReleaseEvent(e)) return;
 
 		// Stop drag view
-#if QT_VERSION < QT_VERSION_CHECK(5, 15, 1) // ### Qt 6: remove
-	if (e->button() == Qt::MidButton)
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 	if (e->button() == Qt::MiddleButton)
-#endif
 	{
 		viewport()->setCursor(Qt::ArrowCursor);
 	}
@@ -614,14 +577,7 @@ void DiagramView::mouseReleaseEvent(QMouseEvent *e)
 			QMenu *menu = new QMenu(this);
 			menu->addAction(act);
 
-#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)	// ### Qt 6: remove
-			menu->popup(e->globalPos());
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 			menu->popup(e->pos());
-#endif
 		}
 
 		m_free_rubberbanding = false;
diff --git a/sources/elementspanelwidget.cpp b/sources/elementspanelwidget.cpp
index 16d95b4f4..8dd782d35 100644
--- a/sources/elementspanelwidget.cpp
+++ b/sources/elementspanelwidget.cpp
@@ -180,7 +180,7 @@ void ElementsPanelWidget::reloadAndFilter()
 }
 
 /**
-	* Emit the requestForProject signal with te selected project
+	* Emit the requestForProject signal with the selected project
 */
 void ElementsPanelWidget::activateProject()
 {
diff --git a/sources/elementtextpattern.cpp b/sources/elementtextpattern.cpp
index f76fae68b..71a2f9586 100644
--- a/sources/elementtextpattern.cpp
+++ b/sources/elementtextpattern.cpp
@@ -59,7 +59,7 @@ ExportElementTextPattern::ExportElementTextPattern(Element *elmt) :
 		return;
 	
 		//Check if a conf with the same name already exist
-	if (QFileInfo::exists(dir.absoluteFilePath(m_name + ".xml")))
+	if (QFileInfo::exists(dir.absoluteFilePath(m_name % ".xml")))
 	{
 		bool r = QMessageBox::question(parentWidget(),
 									   QObject::tr("Configuration de textes"),
@@ -71,7 +71,7 @@ ExportElementTextPattern::ExportElementTextPattern(Element *elmt) :
 	}
 	
 	QDomDocument doc = xmlConf();
-	QET::writeXmlFile(doc, dir.absoluteFilePath(m_name + ".xml"));
+	QET::writeXmlFile(doc, dir.absoluteFilePath(m_name % ".xml"));
 }
 
 /**
@@ -202,7 +202,7 @@ void ImportElementTextPattern::apply(QString name, bool erase) const
 	if(!name.endsWith(".xml"))
 		name.append(".xml");
 	
-	QFile conf_file(QETApp::configDir() + "/element_texts_pattern/" + name);
+	QFile conf_file(QETApp::configDir() % "/element_texts_pattern/" % name);
 	if(!conf_file.open(QIODevice::ReadOnly | QIODevice::Text))
 		return;
 	
diff --git a/sources/exportdialog.cpp b/sources/exportdialog.cpp
index b5a2de519..0a58ed6a2 100644
--- a/sources/exportdialog.cpp
+++ b/sources/exportdialog.cpp
@@ -790,7 +790,7 @@ void ExportDialog::exportDiagram(ExportDiagramLine *diagram_line) {
 	
 	// recupere le format a utiliser (acronyme et extension)
 	QString format_acronym = export_properties.format;
-	QString format_extension = "." + format_acronym.toLower();
+	QString format_extension = "." % format_acronym.toLower();
 	
 	// determine le nom de fichier a utiliser
 	QString diagram_path = diagram_line -> file_name -> text();
@@ -887,7 +887,7 @@ void ExportDialog::slot_checkDiagramsCount()
 void ExportDialog::slot_changeFilesExtension(bool force_extension) {
 	// recupere le format a utiliser (acronyme et extension)
 	QString format_acronym = epw -> exportProperties().format;
-	QString format_extension = "." + format_acronym.toLower();
+	QString format_extension = "." % format_acronym.toLower();
 
 	// set maximum width / height according limitations in QPainter
 	if ((format_extension == ".bmp") ||
@@ -917,11 +917,11 @@ void ExportDialog::slot_changeFilesExtension(bool force_extension) {
 		// cas 2 : l'extension est absente
 		if (diagram_filename_info.suffix().isEmpty()) {
 			if (force_extension) {
-				diagram_filename = diagram_filename_info.completeBaseName() + format_extension;
+				diagram_filename = diagram_filename_info.completeBaseName() % format_extension;
 			}
 		} else {
 			// cas 3 : l'extension est presente mais erronee
-			diagram_filename = diagram_filename_info.completeBaseName() + format_extension;
+			diagram_filename = diagram_filename_info.completeBaseName() % format_extension;
 		}
 		
 		diagram_line -> file_name -> setText(diagram_filename);
@@ -1034,7 +1034,7 @@ ExportDialog::ExportDiagramLine::ExportDiagramLine(Diagram *dia, QSize diagram_s
 	if (diagram_title.isEmpty()) diagram_title = QObject::tr("Folio sans titre");
 	QString diagram_filename = diagram -> title();
 	if (diagram_filename.isEmpty()) diagram_filename = QObject::tr("schema");
-	diagram_filename = QET::stringToFileName(diagram_index % "_" + diagram_filename);
+	diagram_filename = QET::stringToFileName(diagram_index % "_" % diagram_filename);
 	
 	title_label = new QLabel(diagram_title);
 	
diff --git a/sources/exportproperties.cpp b/sources/exportproperties.cpp
index 250632624..191ac0c12 100644
--- a/sources/exportproperties.cpp
+++ b/sources/exportproperties.cpp
@@ -54,24 +54,24 @@ ExportProperties::~ExportProperties()
 void ExportProperties::toSettings(QSettings &settings,
 				  const QString &prefix) const
 {
-	settings.setValue(prefix + "path",
+	settings.setValue(prefix % "path",
 			  QDir::toNativeSeparators(
 				  destination_directory.absolutePath()));
-	settings.setValue(prefix + "format",
+	settings.setValue(prefix % "format",
 			  format);
-	settings.setValue(prefix + "drawgrid",
+	settings.setValue(prefix % "drawgrid",
 			  draw_grid);
-	settings.setValue(prefix + "drawborder",
+	settings.setValue(prefix % "drawborder",
 			  draw_border);
-	settings.setValue(prefix + "drawtitleblock",
+	settings.setValue(prefix % "drawtitleblock",
 			  draw_titleblock);
-	settings.setValue(prefix + "drawterminals",
+	settings.setValue(prefix % "drawterminals",
 			  draw_terminals);
-	settings.setValue(prefix + "drawbgtransparent",
+	settings.setValue(prefix % "drawbgtransparent",
 			  draw_bg_transparent);
-	settings.setValue(prefix + "drawcoloredconductors",
+	settings.setValue(prefix % "drawcoloredconductors",
 			  draw_colored_conductors);
-	settings.setValue(prefix + "area",
+	settings.setValue(prefix % "area",
 			  QET::diagramAreaToString(exported_area));
 }
 
@@ -85,30 +85,30 @@ void ExportProperties::fromSettings(QSettings &settings,
 	QString export_path = QETApp::documentDir();
 	destination_directory.setPath(
 				settings.value(
-					prefix + "path",
+					prefix % "path",
 					export_path).toString());
 	if (!destination_directory.exists())
 		destination_directory.setPath(export_path);
 
-	format = settings.value(prefix + "format").toString();
+	format = settings.value(prefix % "format").toString();
 
-	draw_grid = settings.value(prefix + "drawgrid",
+	draw_grid = settings.value(prefix % "drawgrid",
 				   false).toBool();
-	draw_border = settings.value(prefix + "drawborder",
+	draw_border = settings.value(prefix % "drawborder",
 				     true ).toBool();
-	draw_titleblock = settings.value(prefix + "drawtitleblock",
+	draw_titleblock = settings.value(prefix % "drawtitleblock",
 					 true ).toBool();
-	draw_terminals = settings.value(prefix + "drawterminals",
+	draw_terminals = settings.value(prefix % "drawterminals",
 					false).toBool();
-	draw_bg_transparent = settings.value(prefix + "drawbgtransparent",
+	draw_bg_transparent = settings.value(prefix % "drawbgtransparent",
 					false).toBool();
 	draw_colored_conductors = settings.value(
-				prefix + "drawcoloredconductors",
+				prefix % "drawcoloredconductors",
 				true ).toBool();
 
 	exported_area  = QET::diagramAreaFromString(
 				settings.value(
-					prefix + "area",
+					prefix % "area",
 					"border").toString());
 }
 
diff --git a/sources/machine_info.cpp b/sources/machine_info.cpp
index a7b6322eb..c53ed455e 100644
--- a/sources/machine_info.cpp
+++ b/sources/machine_info.cpp
@@ -55,43 +55,6 @@ void MachineInfo::send_info_to_debug()
 		<< QLibraryInfo::isDebugBuild();
 	qInfo()<< "Qt library version:"
 		<< QLibraryInfo::version();
-#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)	// ### Qt 6: remove
-	qInfo()<< "Qt library location default prefix:"
-		<< QLibraryInfo::location(QLibraryInfo::PrefixPath);
-	qInfo()<< "Qt library location documentation:"
-		<< QLibraryInfo::location(QLibraryInfo::DocumentationPath);
-	qInfo()<< "Qt library location headers:"
-		<< QLibraryInfo::location(QLibraryInfo::HeadersPath);
-	qInfo()<< "Qt library location libraries:"
-		<< QLibraryInfo::location(QLibraryInfo::LibrariesPath);
-	qInfo()<< "Qt library location executables:"
-		<< QLibraryInfo::location(QLibraryInfo::LibraryExecutablesPath);
-	qInfo()<< "Qt library location Qt binaries:"
-		<< QLibraryInfo::location(QLibraryInfo::BinariesPath);
-	qInfo()<< "Qt library location Qt plugins:"
-		<< QLibraryInfo::location(QLibraryInfo::PluginsPath);
-	qInfo()<< "Qt library location installed QML extensions:"
-		<< QLibraryInfo::location(QLibraryInfo::ImportsPath);
-	qInfo()<< "Qt library location installed QML extensions:"
-		<< QLibraryInfo::location(QLibraryInfo::Qml2ImportsPath);
-	qInfo()<< "Qt library location dependent Qt data:"
-		<< QLibraryInfo::location(QLibraryInfo::ArchDataPath);
-	qInfo()<< "Qt library location independent Qt data:"
-		<< QLibraryInfo::location(QLibraryInfo::DataPath);
-	qInfo()<< "Qt library location translation:"
-		<< QLibraryInfo::location(QLibraryInfo::TranslationsPath);
-	qInfo()<< "Qt library location examples:"
-		<< QLibraryInfo::location(QLibraryInfo::ExamplesPath);
-	qInfo()<< "Qt library location Qt testcases:"
-		<< QLibraryInfo::location(QLibraryInfo::TestsPath);
-#ifndef Q_OS_WIN
-	qInfo()<< "Qt library location Qt settings:"
-		<< QLibraryInfo::location(QLibraryInfo::SettingsPath);
-#endif
-#else
-#if TODO_LIST
-#pragma message("@TODO remove code for QT 6 or later")
-#endif
 	qInfo()<< "Qt library path default prefix:"
 		<< QLibraryInfo::path(QLibraryInfo::PrefixPath);
 	qInfo()<< "Qt library path documentation:"
@@ -123,30 +86,29 @@ void MachineInfo::send_info_to_debug()
 #ifndef Q_OS_WIN
 	qInfo()<< "Qt library path Qt settings:"
 		<< QLibraryInfo::path(QLibraryInfo::SettingsPath);
-#endif
 #endif
 	if (strlen(GIT_COMMIT_SHA)) {
-		qInfo() << "GitRevision " + QString(GIT_COMMIT_SHA);
+		qInfo() << "GitRevision " % QString(GIT_COMMIT_SHA);
 	}
-	qInfo()<< "QElectroTech V " + QetVersion::displayedVersion();
-	qInfo()<< QObject::tr("Compilation : ") + pc.built.version;
-	qInfo()<< "Built with Qt " + pc.built.QT
-		  + " - " + pc.built.arch
-		  + " - Date : " + pc.built.date
-		  + " : " + pc.built.time;
-	qInfo()<< "Run with Qt "+ QString(qVersion())
-		  + " using"
-		  + QString(" %1 thread(s)").arg(pc.cpu.ThreadCount);
-	qInfo()<< "CPU : " + pc.cpu.info;
+	qInfo()<< "QElectroTech V " % QetVersion::displayedVersion();
+	qInfo()<< QObject::tr("Compilation : ") % pc.built.version;
+	qInfo()<< "Built with Qt " % pc.built.QT
+		  % " - " % pc.built.arch
+		  % " - Date : " % pc.built.date
+		  % " : " % pc.built.time;
+	qInfo()<< "Run with Qt " % QString(qVersion())
+		  % " using"
+		  % QString(" %1 thread(s)").arg(pc.cpu.ThreadCount);
+	qInfo()<< "CPU : " % pc.cpu.info;
 	qInfo()<< pc.ram.Total;
 	qInfo()<< pc.ram.Available;
-	qInfo()<< "GPU : " + pc.gpu.info;
-	qInfo()<< "GPU RAM : " + pc.gpu.RAM;
+	qInfo()<< "GPU : " % pc.gpu.info;
+	qInfo()<< "GPU RAM : " % pc.gpu.RAM;
 
-	qInfo()<< "OS : " + pc.os.type
-		  + "  - " + pc.cpu.Architecture
-		  + " - Version : "+pc.os.name
-		  + " - Kernel : "+pc.os.kernel;
+	qInfo()<< "OS : " % pc.os.type
+		  % "  - " % pc.cpu.Architecture
+		  % " - Version : " % pc.os.name
+		  % " - Kernel : " % pc.os.kernel;
 	qInfo()<< "";
 	
 	qInfo()<< " OS System language:"<< QLocale::system().name();
@@ -171,8 +133,8 @@ void MachineInfo::send_info_to_debug()
 	qInfo()<< " App Config Location:"<< QETApp::configDir();
 	qInfo()<< " For data-files (user-/company-collections, titleblocks, etc.):";
 	qInfo()<< " App Data Location:"<< QETApp::dataDir();
-	qInfo()<< " Directory for project stalefiles:";
-	qInfo()<< " Generic Data Location:"<< QStandardPaths::writableLocation(QStandardPaths::GenericDataLocation) + "/stalefiles/QElectroTech/";
+	qInfo()<< " Directory for project's autosave files (stalefiles):";
+	qInfo()<< " Autosave:"<< QETApp::autosaveDir() % "/autosave";
 	// qInfo()<< " App Local DataLocation:"<< QStandardPaths::writableLocation(QStandardPaths::ApplicationsLocation);
 	// qInfo()<< " Home Location:"<< QStandardPaths::writableLocation(QStandardPaths::HomeLocation);
 	// qInfo()<< " Runtime Location:"<< QStandardPaths::writableLocation(QStandardPaths::RuntimeLocation);
@@ -452,29 +414,29 @@ int32_t MachineInfo::i_max_screen_height() {
 */
 QString MachineInfo::compilation_info()
 {
-	QString compilation_info = "<br />" + QObject::tr("Compilation :   ");
+	QString compilation_info = "<br />" % QObject::tr("Compilation :   ");
 	compilation_info +=pc.built.version;
 	
-	compilation_info += "<br>Built with Qt " + pc.built.QT;
-	compilation_info += " - " + pc.built.arch;
-	compilation_info += " - Date : " + pc.built.date;
-	compilation_info += " : " + pc.built.time;
+	compilation_info += "<br>Built with Qt " % pc.built.QT;
+	compilation_info += " - " % pc.built.arch;
+	compilation_info += " - Date : " % pc.built.date;
+	compilation_info += " : " % pc.built.time;
 	if (strlen(GIT_COMMIT_SHA)) {
-		compilation_info += "<br> Git Revision : " + QString(GIT_COMMIT_SHA);
+		compilation_info += "<br> Git Revision : " % QString(GIT_COMMIT_SHA);
 	}
-	compilation_info += " <br>Run with Qt " + QString(qVersion());
+	compilation_info += " <br>Run with Qt " % QString(qVersion());
 	compilation_info += " using"
 			+ QString(" %1 thread(s)").arg(pc.cpu.ThreadCount);
-	compilation_info +=  "<br> CPU : " + pc.cpu.info;
-	compilation_info += "<br>" + pc.ram.Total;
-	compilation_info += "<br>" + pc.ram.Available;
-	compilation_info += "<br>GPU : " + pc.gpu.info;
-	compilation_info += "<br>GPU RAM : " + pc.gpu.RAM;
+	compilation_info +=  "<br> CPU : " % pc.cpu.info;
+	compilation_info += "<br>" % pc.ram.Total;
+	compilation_info += "<br>" % pc.ram.Available;
+	compilation_info += "<br>GPU : " % pc.gpu.info;
+	compilation_info += "<br>GPU RAM : " % pc.gpu.RAM;
 
-	compilation_info += "<br>  OS : " + pc.os.type;
-	compilation_info += "  -   " + pc.cpu.Architecture;
-	compilation_info += " -  Version :    "+pc.os.name;
-	compilation_info += "</br> -  Kernel :     "+pc.os.kernel;
+	compilation_info += "<br>  OS : " % pc.os.type;
+	compilation_info += "  -   " % pc.cpu.Architecture;
+	compilation_info += " -  Version :    " % pc.os.name;
+	compilation_info += "</br> -  Kernel :     " % pc.os.kernel;
 	compilation_info += "<br>  *** Qt screens *** </br>";
 
 	for (int ii = 0; ii < pc.screen.count; ++ii) {
diff --git a/sources/machine_info.h b/sources/machine_info.h
index a3a7201b6..9d069792e 100644
--- a/sources/machine_info.h
+++ b/sources/machine_info.h
@@ -84,12 +84,12 @@ class MachineInfo
 			QString version=
 #ifdef __GNUC__
 #ifdef __APPLE_CC__
-					"CLANG " + QString(__clang_version__);
+					"CLANG " % QString(__clang_version__);
 #else
-					"GCC " + QString(__VERSION__);
+					"GCC " % QString(__VERSION__);
 #endif
 #elif defined(Q_CC_MSVC)
-					"MSVC " + QString(QT_STRINGIFY(_MSC_FULL_VER));
+					"MSVC " % QString(QT_STRINGIFY(_MSC_FULL_VER));
 #endif
 			QString QT=QString(QT_VERSION_STR);
 			QString date=QString(__DATE__);