This information is particularly useful when the element has the Rate type:
Ex-tax amount
The system applies the discount or the costs to the tax-excluded amount. Taxes are then applied to this new basis.
Tax incl amount
The principle is that the invoicing element applies to the tax-included amount for an element having the Rate type, or that the amount is a tax-excluded amount for an element expressed in value. This means that the tax detail cannot be determined. In that case, the tax code used originates from the EXETAX - Exempt tax code parameter (TC chapter, VAT group).
When the invoicing element has the Rate type, you can use the Action and Processing fields to define an application basis different from the tax-included or tax-excluded amount.