Form builder's visibleIf property enables you to control the dynamic display of a particular field.

They can be simple expressions such as:

"visibleIf": "field=true"

Or you can combine two conditions together as an AND:

"visibleIf": "field=true,field2=1234"

You can also write complex expressions:

"visibleIf": ":([TestField1=aruba] OR [Testfield2=bob]) AND [toggelfield=true]"

To use expressions, you must:

• Start the visibleIf with a : to say that you're using an expression.
• You must reference form fields inside a [ ], e.g. [SomePicker=1234]. Anything else won't work.
• The AND/OR can be upper or lowercase, it doesn't matter, but they must be surrounded by a space (e.g. [Field1=a] OR [Field2=b] NOT [Field1=a]OR[Field2=b]
• You can use brackets to nest expressions and can have any level of nesting. 
• The : before the OR clause is necessary in the complex expression example.