Update docs

docs/templates/properties.js

@@ -39,6 +39,14 @@ module.exports['has-errors'] = function ({ item }) {
   return item.inheritance.some(c => c.errors.length > 0);
 };
 
+module.exports['internal-variables'] = function ({ item }) {
+  return item.variables.filter(({ visibility }) => visibility === 'internal');
+};
+
+module.exports['has-internal-variables'] = function ({ item }) {
+  return module.exports['internal-variables']({ item }).length > 0;
+};
+
 module.exports.functions = function ({ item }) {
   return [
     ...[...findAll('FunctionDefinition', item)].filter(f => f.visibility !== 'private'),