diff -r 61548f7d1bef -r 7b1db17287b6 svghmi/gen_index_xhtml.ysl2
--- a/svghmi/gen_index_xhtml.ysl2	Fri Feb 28 17:52:35 2020 +0100
+++ b/svghmi/gen_index_xhtml.ysl2	Fri Feb 28 22:54:07 2020 +0100
@@ -200,25 +200,14 @@
     // return overlapping geometry for a given element
     // all intersercting element are returned
     // except groups, that must be contained to be counted in
+    const "groups", "/svg:svg | //svg:g";
+
     def "func:overlapping_geometry" {
         param "elt";
         const "g", "$geometry[@Id = $elt/@id]"; 
         const "candidates", "$geometry[@Id != $elt/@id]";
-        result "$candidates[func:intersect($g, .) = 9]";
-/*
-        const "groups", "$candidates[@Id = //svg:g/@id]"; 
-        const "graphic", "$candidates[@Id != $groups/@Id]"; 
-        result "$groups[func:intersect($g, .) = 9] | $graphic[func:intersect($g, .) > 0]";
-        */
-    }
-
-    def "func:sumarized_elements" {
-        param "elements";
-        const "short_list", "$elements[not(ancestor::*/@id = $elements/@id)]";
-        /* TODO exclude globally discardable elements from group fulfillment check */
-        const "filled_groups", "$short_list/parent::svg:*[not(descendant::*[not(self::svg:g)][not(@id = $short_list/descendant-or-self::*[not(self::svg:g)]/@id)])]";
-        const "groups_to_add", "$filled_groups[not(ancestor::*/@id = $filled_groups/@id)]";
-        result "$groups_to_add | $short_list[not(ancestor::svg:g/@id = $filled_groups/@id)]";
+        result """$candidates[(@Id = $groups/@id and (func:intersect($g, .) = 9)) or 
+                              (not(@Id = $groups/@id) and (func:intersect($g, .) > 0 ))]""";
     }
 
     def "func:all_related_elements" {
@@ -229,6 +218,37 @@
         result "$page_sub_elements";
     }
 
+    def "func:required_elements" {
+        param "pages"; 
+        choose{
+            when "$pages"{
+                result """func:all_related_elements($pages[1])
+                          | func:required_elements($pages[position()!=1])""";
+            }otherwise{
+                result "/..";
+            }
+        }
+    }
+
+    const "required_elements", 
+        """//svg:defs/descendant-or-self::svg:*
+           | func:required_elements($hmi_pages)/ancestor-or-self::svg:*""";
+
+    const "discardable_elements", "//svg:*[not(@id = $required_elements/@id)]";
+
+    def "func:sumarized_elements" {
+        param "elements";
+        const "short_list", "$elements[not(ancestor::*/@id = $elements/@id)]";
+        const "filled_groups", """$short_list/parent::svg:*[
+            not(descendant::*[
+                not(self::svg:g) and 
+                not(@id = $discardable_elements/@id) and
+                not(@id = $short_list/descendant-or-self::*[not(self::svg:g)]/@id)
+            ])]""";
+        const "groups_to_add", "$filled_groups[not(ancestor::*/@id = $filled_groups/@id)]";
+        result "$groups_to_add | $short_list[not(ancestor::svg:g/@id = $filled_groups/@id)]";
+    }
+
     def "func:detachable_elements" {
         param "pages"; 
         choose{
@@ -242,9 +262,8 @@
     }
     
     const "detachable_elements", "func:detachable_elements($hmi_pages)";
-    const "essential_elements", "$detachable_elements | /svg:svg/svg:defs";
-    const "required_elements", "$essential_elements//svg:* | $essential_elements/ancestor-or-self::svg:*";
-    const "discardable_elements", "//svg:*[not(@id = $required_elements/@id)]";
+    // const "essential_elements", "$detachable_elements | /svg:svg/svg:defs";
+    // const "required_elements", "$essential_elements//svg:* | $essential_elements/ancestor-or-self::svg:*";
 
     template "*", mode="index" {
         param "index", "0";
@@ -286,8 +305,8 @@
      */
     template "@* | node()", mode="inline_svg" {
       /* use real xsl:copy instead copy-of alias from yslt.yml2 */
-      xsl:copy apply "@* | node()", mode="inline_svg";
-      /* TODO filter out globally discardable elements */
+      if "not(@id = $discardable_elements/@id)"
+          xsl:copy apply "@* | node()", mode="inline_svg";
     }
 
     /* replaces inkscape's height and width hints. forces fit */