[SCH-TSR-31] MUST have one Key element with the meta scheme ID 'DT'
SCH-TSR-31
/tsr:TransactionStatisticsReport/tsr:Subtotal[normalize-space(@type) = 'PerSP-DT-PR-CC']
count(tsr:Key[normalize-space(@metaSchemeID) = 'DT']) = 1