<grammar xmlns="http://relaxng.org/ns/structure/1.0"> <define name="sum.content"> <ref name="Token.type"/> </define> <define name="sum.token"> <element name="sum"> <ref name="sum.content"/> </element> </define> <define name="product.content"> <ref name="Token.type"/> </define> <define name="product.token"> <element name="product"> <ref name="product.content"/> </element> </define> <define name="limit.content"> <ref name="Token.type"/> </define> <define name="limit.token"> <element name="limit"> <ref name="limit.content"/> </element> </define> <define name="tendsto.content"> <ref name="Token.type"/> <optional> <attribute name="type"> <ref name="MathMLtype"/> </attribute> </optional> </define> <define name="tendsto.token"> <element name="tendsto"> <ref name="tendsto.content"/> </element> </define> </grammar>