添加到@john的答案中(因为注释有字数限制):
这对于VXML 2.1也是如此:
https://www.w3.org/TR/voicexml21/vxml.xsd
<xsd:element name="if">
<xsd:sequence>
<xsd:group ref="executable.content" minOccurs="0" maxOccurs="unbounded"/>
<xsd:sequence minOccurs="0" maxOccurs="unbounded">
<xsd:element ref="elseif"/>
<xsd:group ref="executable.content" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
<xsd:sequence minOccurs="0" maxOccurs="1">
<xsd:element ref="else"/>
<xsd:group ref="executable.content" minOccurs="0" maxOccurs="unbounded"/>
</xsd:sequence>
</xsd:sequence>
<xsd:attributeGroup ref="If.attribs"/>
</xsd:complexType>
</xsd:element>