customizedFields support for f:checkbox (and thus also f:optionalBlock).

core/src/main/resources/lib/form/checkbox.jelly

@@ -56,15 +56,21 @@ THE SOFTWARE.
     </st:attribute>
   </st:documentation>
   <f:prepareDatabinding />
+  <j:set var="name" value="${attrs.name ?: '_.'+attrs.field}"/>
+  <j:set var="default" value="${attrs.default ?: false}"/>
+  <j:set var="value" value="${attrs.checked ?: instance[attrs.field] ?: default}"/>
   <input type="checkbox"
-         name="${attrs.name?:'_.'+attrs.field}"
+         name="${name}"
          value="${attrs.value}"
          title="${attrs.tooltip}"
          onclick="${attrs.onclick}" id="${attrs.id}" class="${attrs.negative!=null ? 'negative' : null} ${attrs.checkUrl!=null?'validated':''}"
          checkUrl="${attrs.checkUrl}" checkDependsOn="${attrs.checkDependsOn}" json="${attrs.json}"
-         checked="${(attrs.checked ?: instance[attrs.field] ?: attrs.default) ? 'true' : null}"/>
+         checked="${value ? 'true' : null}"/>
   <j:if test="${attrs.title!=null}">
     <label class="attach-previous"
            title="${attrs.tooltip}">${attrs.title}</label>
   </j:if>
+  <j:if test="${customizedFields != null and value != default}">
+    <j:mute>${customizedFields.add(name)}</j:mute>
+  </j:if>
 </j:jelly>