Recurring Data Types / Namespaces?

Is it legal for a parent node to have multiple child nodes with the same reference type? Here is an example of what I am referring to. CreditSurchargeDt and SecondaryCD occur twice in this sequence. I would think this would be illegal but I would like some confirmation please. If this is illegal, why and how should it be written? Is this a namespace violation?

<group name="PCCREDITSURCHARGE">

       <sequence minOccurs="0" maxOccurs="1">

            <element ref="CreditSurchargeDt" minOccurs="0" maxOccurs="1"/> 


            <element ref="SecondaryCd" minOccurs="0" maxOccurs="1"/> 

            <element ref="CreditSurchargeDt" minOccurs="0" maxOccurs="1"/>

            <element ref="DiscountSurchargeFactorCd"/>

            <element ref="Amount" minOccurs="0" maxOccurs="1"/>

            <element ref="IterationNumber" minOccurs="0" maxOccurs="1"/>

            <element ref="SecondaryCd" minOccurs="0" maxOccurs="1"/>

      </sequence>

</group>