Get the next Child, if anyreturnthe next Child; may return null
Get the previous Child, if anyreturnthe previous Child; may return null
Set the next Childparamchild the new 'next' child; may be null, which has the effect of saying there is no 'next' child
Set the previous Childparamchild the new 'previous' child; may be null, which has the effect of saying there is no 'previous' child