XML Validation - What's good for XSD good for DTD? Need XML Expert?

Take the following XML File:
<?xml version="1.0"?>
<root>
<metric_item>
<quantity>63</quantity>
</metric_item>
<english_item>
<quantity>One Bushel</quantity>
</english_item>
</root>

In XSD, this can be easily verified:
<xsd:schema xmlns:xsd=".....">
<xsd:element name="root">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="metric_item">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="quantity" type="xsd:integer"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
<xsd:element name="english_item">
<xsd:complexType>
<xsd:sequence>
<xsd:element name="quantity" type="xsd:string"/>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:sequence>
</xsd:complexType>
</xsd:element>
</xsd:schema>

But in DTDs, I'm not sure if can be done (w/o namespace at least). If no, is it considered "bad form" or "bad design"? Should all XML docs be DTD-verifiable?