Class ParagraphTextValidation

// Add a paragraph text item to a form and require the answer to be at least 100 characters.
var paragraphTextItem = form.addParagraphTextItem().setTitle('Describe yourself:');
var paragraphtextValidation = FormApp.createParagraphTextValidation()
  .setHelpText(“Answer must be more than 100 characters.”)
  .requireTextLengthGreaterThanOrEqualTo(100).build();
paragraphTextItem.setValidation(paragraphtextValidation);