diff --git a/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-add.xsl b/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-add.xsl
index 771e0259388..522aa82815b 100644
--- a/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-add.xsl
+++ b/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-add.xsl
@@ -182,6 +182,7 @@ Note: It assumes that it will be adding new items in
 
   <!-- Updating the gmd:onLine based on update parameters -->
   <!-- Note: first part of the match needs to match the xsl:for-each select from extract-relations.xsl in order to get the position() to match -->
+  <!-- The unique identifier is marked with resourceIdx which is the position index and resourceHash which is hash code of the current node (combination of url, resource name, and description) -->
   <xsl:template
     match="*//gmd:MD_DigitalTransferOptions/gmd:onLine
         [gmd:CI_OnlineResource[gmd:linkage/gmd:URL!=''] and ($resourceIdx = '' or position() = xs:integer($resourceIdx))]
diff --git a/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-remove.xsl b/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-remove.xsl
index 194eb2c530f..f273ed80450 100644
--- a/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-remove.xsl
+++ b/schemas/iso19139/src/main/plugin/iso19139/process/onlinesrc-remove.xsl
@@ -52,6 +52,7 @@ Stylesheet used to remove a reference to a online resource.
 
   <!-- Remove the gmd:onLine define in url parameter  -->
   <!-- Note: first part of the match needs to match the xsl:for-each select from extract-relations.xsl in order to get the position() to match -->
+  <!-- The unique identifier is marked with resourceIdx which is the position index and resourceHash which is hash code of the current node (combination of url, resource name, and description) -->
   <xsl:template
     match="*//gmd:MD_DigitalTransferOptions/gmd:onLine
         [gmd:CI_OnlineResource[gmd:linkage/gmd:URL!=''] and ($resourceIdx = '' or (count(preceding::gmd:onLine) + 1) = xs:integer($resourceIdx))]
diff --git a/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-add.xsl b/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-add.xsl
index f4bb3eea6d9..b9a42637139 100644
--- a/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-add.xsl
+++ b/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-add.xsl
@@ -97,6 +97,7 @@
 
   <!-- Updating the gmd:graphicOverview based on update parameters -->
   <!-- Note: first part of the match needs to match the xsl:for-each select from extract-relations.xsl in order to get the position() to match -->
+  <!-- The unique identifier is marked with resourceIdx which is the position index and resourceHash which is hash code of the current node (combination of url, resource name, and description) -->
   <xsl:template
     priority="2"
     match="*//gmd:graphicOverview
diff --git a/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-remove.xsl b/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-remove.xsl
index 5a4923fa48d..d87a74739f5 100644
--- a/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-remove.xsl
+++ b/schemas/iso19139/src/main/plugin/iso19139/process/thumbnail-remove.xsl
@@ -47,6 +47,7 @@
 
   <!-- Remove the thumbnail define in thumbnail_url parameter -->
   <!-- Note: first part of the match needs to match the xsl:for-each select from extract-relations.xsl in order to get the position() to match -->
+  <!-- The unique identifier is marked with resourceIdx which is the position index and resourceHash which is hash code of the current node (combination of url, resource name, and description) -->
   <xsl:template
     priority="4"
     match="*//gmd:graphicOverview