Combo represents the tax combination of a category code and rate key.
|Category||cbc.Code||true||Tax category code from those available inside a region.|
|Rate||cbc.Key||Rate within a category to apply.|
|Percent||num.Percentage||Percent defines the percentage set manually or determined from the rate key (calculated if rate present).|
|Surcharge||num.Percentage||Some countries require an additional surcharge (calculated if rate present).|
|Ext||cbc.CodeMap||Local codes that apply for a given rate or percentage that need to be identified and validated.|