sentences:  The credit generally applies only to taxes of a nature similar to the tax being reduced by the credit (taxes based on income) and is often limited to the amount of tax attributable to foreign source income.The limitation may be computed by country, class of income, overall, and/or another manner.Most income tax systems therefore contain rules defining source of income (domestic, foreign, or by country) and timing of recognition of income, deductions, and taxes, as well as rules for associating deductions with income.