diff --git a/extension.json b/extension.json
index 5acc10517..a94a00aed 100644
--- a/extension.json
+++ b/extension.json
@@ -121,6 +121,7 @@
 				"ve.ui.MWCitationAction.js",
 				"ve.ui.MWReference.init.js",
 				"ve.ui.MWCitationNeededContextItem.js",
+				"ve.ui.MWSetExtendsContentDialog.js",
 				{
 					"name": "ve.ui.contentLanguage.js",
 					"callback": "Cite\\ResourceLoader\\ContentLanguage::makeScript"
@@ -131,7 +132,8 @@
 				"ve.ui.MWReferenceContextItem.less",
 				"ve.ui.MWReferenceResultWidget.less",
 				"ve.ui.MWReferenceSearchWidget.less",
-				"ve.ui.MWCitationDialogTool.less"
+				"ve.ui.MWCitationDialogTool.less",
+				"ve.ui.MWSetExtendsContentDialog.less"
 			],
 			"dependencies": [
 				"oojs-ui.styles.icons-alerts",
diff --git a/modules/ve-cite/ve.ui.MWSetExtendsContentDialog.js b/modules/ve-cite/ve.ui.MWSetExtendsContentDialog.js
new file mode 100644
index 000000000..f60c4664e
--- /dev/null
+++ b/modules/ve-cite/ve.ui.MWSetExtendsContentDialog.js
@@ -0,0 +1,155 @@
+'use strict';
+
+/*!
+ * VisualEditor UserInterface MWSetExtendsContentDialog class.
+ *
+ * @copyright 2024 VisualEditor Team's Cite sub-team and others; see AUTHORS.txt
+ * @license MIT
+ */
+
+/**
+ * Dialog for inserting a sub-reference from a main reference
+ *
+ * @class
+ * @extends OO.ui.ProcessDialog
+ *
+ * @constructor
+ * @param {Object} [config] Configuration options
+ */
+ve.ui.MWSetExtendsContentDialog = function VeUiMWSetExtendsContentDialog( config ) {
+	// Parent constructor
+	ve.ui.MWSetExtendsContentDialog.super.call( this, config );
+};
+
+/* Inheritance */
+
+OO.inheritClass( ve.ui.MWSetExtendsContentDialog, OO.ui.ProcessDialog );
+
+/* Static Properties */
+
+ve.ui.MWSetExtendsContentDialog.static.name = 'setExtendsContent';
+
+ve.ui.MWSetExtendsContentDialog.static.size = 'medium';
+
+// TODO extends i18n
+ve.ui.MWSetExtendsContentDialog.static.title = 'Extend a reference';
+
+ve.ui.MWSetExtendsContentDialog.static.actions = [
+	{
+		action: 'insert',
+		label: OO.ui.deferMsg( 'visualeditor-dialog-action-insert' ),
+		flags: [ 'progressive', 'primary' ],
+		modes: 'insert'
+	},
+	{
+		label: OO.ui.deferMsg( 'visualeditor-dialog-action-cancel' ),
+		flags: [ 'safe', 'close' ],
+		modes: [ 'insert' ]
+	}
+];
+
+/* Methods */
+
+/**
+ * @inheritdoc
+ */
+ve.ui.MWSetExtendsContentDialog.prototype.initialize = function () {
+	// Parent method
+	ve.ui.MWSetExtendsContentDialog.super.prototype.initialize.apply( this, arguments );
+
+	this.editPanel = new OO.ui.PanelLayout( {
+		scrollable: true, padded: true
+	} );
+
+	// Icon message widget
+	this.extendsWarning = new OO.ui.MessageWidget( {
+		icon: 'alert',
+		inline: true,
+		classes: [ 've-ui-setExtendsContentDialog-warning' ]
+	} );
+
+	this.referenceTarget = ve.init.target.createTargetWidget(
+		{
+			includeCommands: null,
+			excludeCommands: ve.ui.MWReferenceEditPanel.static.getExcludeCommands(),
+			importRules: ve.ui.MWReferenceEditPanel.static.getImportRules(),
+			inDialog: this.constructor.static.name,
+			// TODO extends i18n
+			placeholder: 'Write or paste the content for the extension here'
+		}
+	);
+
+	this.contentFieldset = new OO.ui.FieldsetLayout();
+	this.contentFieldset.$element.append( this.referenceTarget.$element );
+
+	this.editPanel.$element.append( this.extendsWarning.$element, this.contentFieldset.$element );
+
+	this.$body.append( this.editPanel.$element );
+};
+
+/**
+ * @inheritdoc
+ */
+ve.ui.MWSetExtendsContentDialog.prototype.getSetupProcess = function ( data ) {
+	return ve.ui.MWSetExtendsContentDialog.super.prototype.getSetupProcess.call( this, data )
+		.next( () => {
+			this.originalRef = data.originalRef;
+			this.newRef = data.newRef;
+
+			const parentItemNode = data.internalList.getItemNode( this.originalRef.getListIndex() );
+			const $parentRefPreview = new ve.ui.MWPreviewElement( parentItemNode, { useView: true } ).$element;
+			this.extendsWarning.setLabel(
+				$( '<p>' )
+					.text( mw.msg( 'cite-ve-dialog-reference-editing-extends' ) )
+					.append( $parentRefPreview )
+			);
+
+			this.referenceTarget.setDocument( this.newRef.getDocument() );
+		} );
+};
+
+/**
+ * @override
+ */
+ve.ui.MWSetExtendsContentDialog.prototype.getActionProcess = function ( action ) {
+	if ( action === 'insert' ) {
+		return new OO.ui.Process( () => {
+			this.close( { action: action } );
+		} );
+	}
+	return ve.ui.MWSetExtendsContentDialog.super.prototype.getActionProcess.call( this, action );
+};
+
+/**
+ * @inheritdoc
+ */
+ve.ui.MWSetExtendsContentDialog.prototype.getReadyProcess = function ( data ) {
+	return ve.ui.MWSetExtendsContentDialog.super.prototype.getReadyProcess.call( this, data )
+		.next( () => {
+			this.referenceTarget.focus();
+		} );
+};
+
+/**
+ * @inheritdoc
+ */
+ve.ui.MWSetExtendsContentDialog.prototype.getTeardownProcess = function ( data ) {
+	return ve.ui.MWSetExtendsContentDialog.super.prototype.getTeardownProcess.call( this, data )
+		.next( () => {
+			if ( data && data.action && data.action === 'insert' ) {
+				this.newRef.setDocument( this.referenceTarget.getContent() );
+			}
+			this.referenceTarget.clear();
+		} );
+};
+
+/**
+ * @inheritdoc
+ */
+ve.ui.MWSetExtendsContentDialog.prototype.getBodyHeight = function () {
+	return 250;
+};
+
+/* Registration */
+
+ve.ui.windowFactory.register( ve.ui.MWSetExtendsContentDialog );
diff --git a/modules/ve-cite/ve.ui.MWSetExtendsContentDialog.less b/modules/ve-cite/ve.ui.MWSetExtendsContentDialog.less
new file mode 100644
index 000000000..a81463bd6
--- /dev/null
+++ b/modules/ve-cite/ve.ui.MWSetExtendsContentDialog.less
@@ -0,0 +1,11 @@
+/*!
+ * VisualEditor UserInterface MWSetExtendsContentDialog styles.
+ *
+ * @copyright 2024 VisualEditor Team's Cite sub-team and others; see AUTHORS.txt
+ * @license MIT
+ */
+
+.ve-ui-setExtendsContentDialog-warning {
+	font-weight: normal;
+	margin-bottom: 1em;
+}