Hello, We are the team of PHP developers. Our skills includes HTML5, jquery , XML, PHP, Joomla, Wordpress etc. We understand your requirement that you want to have an option where user can check multiple box and if they want to provide additional information which is not available in check box, there will be text box below multiple check boxes that allows them to enter text with max 300 word limit. We can do this task in 1-2 days. Can you please share the website details where you want to add this option. Let me know if you have any queries or we can discuss over freelancer or Skype.
Looking forward to hear from you soon. Thanks