code: @Override
      protected void doProcess(ITemplateContext context, IProcessableElementTag tag, AttributeName attributeName, String attributeValue,
              IElementTagStructureHandler structureHandler) {
          final String name = attributeName.getAttributeName();
          final ExceptionMessageBuilder br = new ExceptionMessageBuilder();
          br.addNotice("Mistaking prefix for the Lasta Thymeleaf name.");
          br.addItem("Advice");
          br.addElement("Use formal prefix for Lasta Thymeleaf 'la:' like this:");
          br.addElement("  (x):");
          br.addElement("    th:" + name + "=\"...\" // *Bad");
          br.addElement("  (o):");
          br.addElement("    la:" + name + "=\"...\" // Good");
          br.addItem("Template File");
          br.addElement(tag.getTemplateName());
          br.addItem("Tag Name");
          br.addElement(tag.getElementDefinition());
          br.addItem("Attribute on Tag");
          br.addElement(attributeName + "=\"" + tag.getAttributeValue(attributeName) + "\"");
          final String msg = br.buildExceptionMessage();
          throw new IllegalStateException(msg);
      }
docs: =======