[DFDL-WG] Better way to model "empty"?

[Garriss Jr., James P.]

A return path email header can take two forms:


1.     Plain email form:        Return-path: <steve at tresys.com>

2.     Empty form:               Return-path: <>

I've found 2 different ways to model this:

#1 - with a choice

                        <xsd:choice>
                                    <xsd:element name="Empty" type="xsd:string" dfdl:lengthKind="explicit" dfdl:length="0"/>
                                    <xsd:element name="PlainEmail" type="PlainEmail"/>
                        </xsd:choice>

#2 - with min/maxOccurs

                        <xsd:element name="PlainEmail" type="PlainEmail" minOccurs="0" maxOccurs="1" dfdl:occursCountKind="implicit"/>

When I'm faced with selecting one of these implementations over another, how do I think?  What criteria should I be using?

Is there another, better way that I haven't even thought of?

TIA
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