Attribute Functions
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  * Function: void rdfSetAttribute(RdfElement *element, const char *attname, const char *value)

     Sets an element's attribute.

       - element: The element containing the attribute.

       - attname: The name of the attribute.

       - value: The attribute's value.

  * Function: char *rdfGetAttribute(RdfElement *element, const char *attname)

     Returns an attribute's value.

     Note: The returned attribute must be freed.

       - element: The element containing the attribute.

       - attname: The name of the attribute.

  * Function: void rdfSetNsAttribute(RdfElement *element, const char *attname, const char *value, RdfNamespace *ns)

     Sets the value of an attribute in the specified namespace.

       - element: The element containing the attribute.

       - attname: The name of the attribute.

       - value: The attribute's value.

  * Function: char *rdfGetNsAttribute(RdfElement *element, const char *attname, RdfNamespace *ns)

     Returns the value of an attribute in the specified namespace.

     Note: The returned attribute must be freed.

       - element: The element containing the attribute.

       - attname: The name of the attribute.

       - ns: The namespace of the attribute.