pack.padding()

pack.padding([padding])

If padding is specified, sets this pack layout’s padding accessor to the specified number or function or returns this pack layout. If padding is not specified, returns the current padding accessor, which defaults to the constant zero. When siblings are packed, tangent siblings will be separated by approximately the specified padding; the enclosing parent circle will also be separated from its children by approximately the specified padding. If an explicit radius is not specified, the padding is approximate because a two-pass algorithm is needed to fit within the layout size: the circles are first packed without padding; a scaling factor is computed and applied to the specified padding; and lastly the circles are re-packed with padding.