should informal invitations be enclosed in a box?
Yes, the invitation should be written inside the box. Please follow the link below to study the proper format of formal and informal invitations:
https://www.meritnation.com/ask-answer/question/could-you-please-tell-me-the-format-of-formal-and-informal-i/english/3960680
https://www.meritnation.com/ask-answer/question/could-you-please-tell-me-the-format-of-formal-and-informal-i/english/3960680