allocation of an expense to a class of income if the expense directly relates to such class, and apportionment of an expense related to multiple classes. Specific rules are provided for certain categories of more fungible expenses, such as interest. By their nature, rules for allocation and apportionment of expenses may become complex. They may incorporate cost accounting or branch accounting principles, or may define new principles. Thin capitalization Most jurisdictions provide that taxable income may be reduced by amounts expended as interest on loans. By contrast, most do not provide tax relief for distributions to owners. Thus, an enterprise is motivated to finance its subsidiary enterprises through loans rather than capital. Many jurisdictions have adopted "thin capitalization" rules to limit such charges. Various approaches include limiting deductibility of interest expense to a portion of cash flow, disallowing interest expense on debt in excess of a certain ratio, and other mechanisms. Enterprise restructure The organization or reorganization of portions of a multinational enterprise often gives rise to events that, absent rules to the contrary, may be taxable in a particular system. Most systems contain rules preventing recognition of income or loss from certain types of such events. In the simplest form, contribution of business assets to a subsidiary enterprise may, in certain circumstances, be treated as a nontaxable event. Rules on structuring and restructuring tend to be highly complex. Credits for taxes of other jurisdictions Systems that tax income from outside the system's jurisdiction tend to provide for a unilateral credit or offset for taxes paid to other jurisdictions. Such other jurisdiction taxes are generally referred to within the system as "foreign" taxes. Tax treaties often require this credit. A credit for foreign taxes is subject to manipulation by planners if there are no limits, or weak limits, on such credit. Generally, the credit is at least limited to the tax within the system that the taxpayer would pay on income from outside the jurisdiction. The credit may be limited by category of income, by other jurisdiction or country, based on an effective tax rate, or otherwise. Where the foreign tax credit is limited, such limitation may involve computation of taxable income from other jurisdictions. Such computations tend to rely heavily on the source of income and allocation of expense rules of the system. Withholding tax Many jurisdictions require persons paying amounts to nonresidents to collect tax due from a