Add comments to explain what empty labels do

data/keyboards/symbols/nb.xml

@@ -65,6 +65,8 @@
     <symbol keyval="197" label="&#197;">Aring</symbol>
     <symbol label=""></symbol>
     <symbol label=""></symbol>
+    <!-- Empty labels cause keys to be hidden when the level they are defined
+         for is shown. -->
   </key>
   <key name="AC01">
     <symbol label="a">a</symbol>

data/keyboards/symbols/us.xml

@@ -115,6 +115,8 @@
     <symbol label="{">braceleft</symbol>
   </key>
   <key name="AC10">
+    <!-- Empty labels cause keys to be hidden when the level they are defined
+         for is shown. -->
     <symbol label=""></symbol>
     <symbol label=""></symbol>
     <symbol label=")">parenright</symbol>

eek/eek-section.c

@@ -535,7 +535,8 @@ keycounter (EekElement *element, gpointer user_data)
 {
     EekKey *key = EEK_KEY(element);
 
-    /* Skip keys without labels for the current level. */
+    /* Skip keys without labels for the current level. This causes those
+       keys to be hidden in the visible layout. */
     if (!eek_key_has_label(key))
         return;