Is SARS definition of 'taxable income' circular with respect to donations made?

According to SARS, "Deductions in respect of donations to certain public benefit organisations are limited to 10% of taxable income (excluding retirement fund lump sums and severance benefits)". But taxable income is the difference between gross income and deductions, one of which is the amount donated. So the SARS definition is circular, and therefore impossible to calculate. Or am I missing something?

For these purposes Taxable Income is before donations allowed.

Thanks guys - much appreciated :)
Pity SARS themselves can't be a bit more helpful in their documentation - always dangerous to assume 'everybody knows that!'.