What are the advantages/disadvantages of using a choice of a several
"sub-"elements with empty content (and no attributes) vs. simple
content.  Here's an example:

Using simple content:
<process>xyz</process>

Using empty content sub-element:
<process><xyz/></process>

Assume in both cases the xyz part has a limited domain, i.e., it can
be xyz, abc, or efg, but no other values make sense.  Of course some
day, I might want to extend it to include rst.

The XML Schema for the empty content sub-element version looks
something like this:

<xsd:complexType name="ProcessType>
   <xsd:complexContent/>
</xsd:complexType>

This defines ProcessType as having empty content.  I can then use this
to define the types of processing I want to allow as follows:

<xsd:element name = "process" type="ProcessChoiceType"/>

<xsd:complexType name="ProcessChoiceType">
   <xsd:complexContent>
      <xsd:choice minOccurs="1" maxOccurs="1">
         <xsd:element name="abc" type="ProcessType"/>
         <xsd:element name="efg" type="ProcessType"/>
         <xsd:element name="xyz" type="ProcessType"/>
         <xsd:element name="extented_process" type="ProcessType"
abstract="true"/>
      </xsd:choice>
   </xsd:complexContent>
</xsd:complexType>

The abstract element extended_process is added to permit extension.
Then I can add new types of processing as follows:

<xsd:element name="rst" substitutionGroup="extended_process"/>

The XML Schema for the simple content version would replace the above
definition of ProcessChoiceType with the following:

<xsd:simpleType name="ProcessChoiceType">
   <xsd:restriction base="xsd:token">
      <xsd:enumeration value="abc"/>
      <xsd:enumeration value="efg"/>
      <xsd:enumeration value="xyz"/>
   <xsd:restriction/>
</xsd:simpleType>

My understanding is the only way to extend the enumeration is to
define a new type, NewProcessChoiceType, using a union.  However, I
don't know of any way to change the declaration of the <process>
element to use this new type.

So my initial analysis is that the empty content sub-elements are more
extensible.  However, I've only been seriously studying XML Schema for
about a week.  So I'm looking for guidance on these two choices.  I
understand that a third alternative would be to use an attribute,
e.g., <process name="xyz"/>, but I don't think I can restrict the
domain of the name attribute using XML Schema, which defeats the whole
point of this discussion.

Thanks in advance for your opinions.