(a) General rule.--All or any part of the estate of a decedent not effectively disposed of by will or otherwise passes to his heirs as prescribed in this chapter, except as modified by the decedent's will.

(b) Modification by decedent's will.--A decedent by will may expressly exclude or limit the right of an individual or class to succeed to property of the decedent passing by intestate succession. If that individual or a member of that class survives the decedent, the share of the decedent's intestate estate to which the individual or class would have succeeded passes as if that individual or each member of that class had disclaimed his intestate share.