Sometimes it can be helpful to visually seperate the form into different sections. The line field is perfect here. It will draw a horizontal rule with enough white space around it to separate sets of fields nicely.
fields: line: type: line
If you want to add multiple lines to your form, make sure that the names for each field are unique:
fields: … line-a: type: line … line-b: type: line … line-c: type: line