You can create a custom validation to check if the content in textarea is less then 10 lines. If you are interested only to resize the textarea you can add a custom class using granite:class and add the required css rule for the height.
You can create a custom validation to check if the content in textarea is less then 10 lines. If you are interested only to resize the textarea you can add a custom class using granite:class and add the required css rule for the height.