private Class getClassFromStack() {
    Object o = stack.peek();
    if (!(o instanceof String)) {
      throw new CacheXmlException(
          "A string class-name was expected, but not found while parsing.");
    }
    String className = (String) stack.pop();

    try {
      Class c = InternalDataSerializer.getCachedClass(className);
      return c;
    } catch (Exception e) {
      throw new CacheXmlException(
          String.format("Unable to load class %s", className), e);
    }
  }
When we have finished a function element, we create the Declarable and push it onto stack
geode-core/src/main/java/org/apache/geode/internal/cache/xmlcache/CacheXmlParser.java