diff --git a/api/src/Etemplate.php b/api/src/Etemplate.php
index b9f09f373a..fac9520b28 100644
--- a/api/src/Etemplate.php
+++ b/api/src/Etemplate.php
@@ -31,6 +31,10 @@ class Etemplate extends Etemplate\Widget\Template
 	 */
 	public $sitemgr=false;
 
+	/**
+	 * @var array Additional attributes to set on the DOM (eg: slot)
+	 */
+	protected $dom_attributes = [];
 	/**
 	 * Tell egw framework it's ok to call this
 	 */
@@ -264,7 +268,12 @@ class Etemplate extends Etemplate\Widget\Template
 				}
 				else
 				{
-					$content = '<form target="egw_iframe_autocomplete_helper" action="'.$form_action.'" id="'.$dom_id.'" class="et2_container"></form>'."\n".
+					$content = '<form target="egw_iframe_autocomplete_helper" action="' . $form_action . '" id="' . $dom_id . '" class="et2_container"' .
+						array_reduce(array_keys($this->dom_attributes), function ($carry, $key)
+						{
+							return "$carry $key=\"" . htmlspecialchars($this->dom_attributes[$key]) . "\"";
+						},           '') .
+						'></form>' . "\n" .
 						'<iframe name="egw_iframe_autocomplete_helper" style="width:0;height:0;position: absolute;visibility:hidden;"></iframe>';
 				}
 				$GLOBALS['egw']->framework->response->generic("data", array($content));
@@ -582,6 +591,11 @@ class Etemplate extends Etemplate\Widget\Template
 		$this->dom_id = $new_id;
 	}
 
+	public function set_dom_attributes($dom_attributes)
+	{
+		$this->dom_attributes = array_merge($this->dom_attributes, $dom_attributes);
+	}
+
 	/**
 	 * Make sure there's a new request, in case of multiple Etemplates in one call.
 	 * Normally this isn't a problem, but if you've got an etemplate in the sidebox,
diff --git a/calendar/inc/class.calendar_ui.inc.php b/calendar/inc/class.calendar_ui.inc.php
index 43b1f4aa32..de1c926fc4 100644
--- a/calendar/inc/class.calendar_ui.inc.php
+++ b/calendar/inc/class.calendar_ui.inc.php
@@ -536,6 +536,7 @@ class calendar_ui
 	{
 		Etemplate::reset_request();
 		$sidebox = new Etemplate('calendar.sidebox');
+		$sidebox->set_dom_attributes(['slot' => 'left']);
 
 		$cont = $this->cal_prefs['saved_states'];
 		if (!is_array($cont)) $cont = array();
diff --git a/calendar/js/app.ts b/calendar/js/app.ts
index dc2acad1d1..ece5510b9a 100644
--- a/calendar/js/app.ts
+++ b/calendar/js/app.ts
@@ -281,7 +281,10 @@ export class CalendarApp extends EgwApp
 			case 'calendar.sidebox':
 				this.sidebox_et2 = _et2.widgetContainer;
 				this.sidebox_hooked_templates.push(this.sidebox_et2);
-				jQuery(_et2.DOMContainer).hide();
+				if(!_et2.DOMContainer.slot)
+				{
+					jQuery(_et2.DOMContainer).hide();
+				}
 
 				this._setup_sidebox_filters();