How can I create a checkbox that has an editable list inside its object? (image included)

I'm trying to add into a modal-- a checkbox that when checked, it gives the user the ability to add/remove an inputted/typed line to the list. Each line can be removed 'x' or add another line with '+'. I have looked into HTML5 form controls, but it's hard to find an obvious way to implement this.

I apologize for the poor description, this wireframe might better explain:

I'd really appreciate some help! Thanks.