Well formed XML and not empty self closed elements

Question

Can a xml be well formed having not empty elements self closed?

Anything like this:

<team>Chicago Bulls<playerA/>23<playerB/>43</team>

instead of:

<team>Chicago Bulls<playerA>23</playerA><playerB>43</playerB></team>

Would it be well formed and where I could read about it? Mostly from w3c.

Thanks in advance

Answer 1

Yes, both of your examples are well-formed, but to precede a player number with a player element rather than place it in the contents of the player element would be a very poor design decision as it would fail to leverage the natural hierarchy that XML tools and developers would expect.

You can read more about well-formedness,

• 2.1 Well-Formed XML Documents
• Is there any difference between 'valid xml' and 'well formed xml'?

but do not expect to see your point addressed explicitly because your question is less about well-formedness than it is about design.

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Historical Note

XML's predecessor, SGML, had a notion of omitted end tags, which might be related to the motivation for your question. Instead of as in your first example where you use self-closing tags (which produce empty elements, to be clear),

<team>Chicago Bulls<playerA/>23<playerB/>43</team>

the playerA and playerB elements could be defined to have an omitted end tags, allowing the following markup:

<team>Chicago Bulls<playerA>23<playerB>43</team>

Your self-closing player elements have been replaced by open tags with omitted end tags. This would not be well-formed XML.

Answer 2

The XML you show is well-formed, but there are no "non-empty self-closed elements". If we add some whitespace, we can show the relationships between nodes:

<team>
   Chicago Bulls
   <playerA/>
   23
   <playerB/>
   43
</team>

So, the team element has 5 child nodes:

1. A text node containing "Chicago Bulls"
2. An element called playerA with no attributes or content
3. A text node containing "23"
4. An element called playerB with no attributes or content
5. A text node containing "43"

No relationship between these nodes is represented, other than their order - in particular, the text "23" is not associated with either of the self-closing elements.

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Another way to show this is to remember that <foo/> is just a different way of writing <foo></foo>, so we can also write this:

<team>Chicago Bulls<playerA></playerA>23<playerB></playerB>43</team>

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In contrast, systematically adding whitespace to your second example would look like this:

<team>
    Chicago Bulls
    <playerA>
        23
    </playerA>
    <playerB>
       43
    </playerB>
</team>

In this case, the teams element has only three direct children:

1. A text node containing "Chicago Bulls"
2. An element called playerA, which contains a text node containing "23"
3. An element called playerB, which contains a text node containing "43"