The term distributable net income has no application except in the taxation of estates and trusts and their beneficiaries. It limits the deductions allowable to estates and trusts for amounts paid, credited, or required to be distributed to beneficiaries and is used to determine how much of an amount paid, credited, or required to be distributed to a beneficiary will be includible in his gross income. It is also used to determine the character of distributions to the beneficiaries. Distributable net income means for any taxable year, the taxable income (as defined in section 63) of the estate or trust, computed with the modifications set forth in §§ 1.643(a)-1 through 1.643(a)-7.