Background

Recently I had a need to comment out whole sections from an XML Document.

XML

Sample XML Document

DTD Internal

sample.dtd.internal.xml

<?xml 
	version = "1.0" 
	encoding = "UTF-8" 
	standalone = "yes" 
?>

<!DOCTYPE address [
   <!ELEMENT address (name,company,phone)>
   <!ELEMENT name (#PCDATA)>
   <!ELEMENT company (#PCDATA)>
   <!ELEMENT phone (#PCDATA)>
]>

<address>
  
   <name>Tom Peters</name>
  
   <company>Fidelity Investments</company>
   
   <phone>710-181-1910</phone>

</address>

DTD External

address.dtd

<!ELEMENT address (name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>

sample.dtd.external.xml

<?XML 
     version = "1.0" 
     encoding = "UTF-8" 
     standalone = "no" 
?>

<!DOCTYPE address SYSTEM "address.dtd">

<address>

<name>Tom Peters</name>

<company>Fidelity Investments</company>

<phone>650-191-9101</phone>

</address>

 

 

DTD External – Adding new Element – Finance

Outline

We will trigger an error by intentionally trying to add an element ( industry ) that is not defined in our DTD file.

address.dtd

<!ELEMENT address (name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>

sample.dtd.external.element.added.finance.xml

<?xml 
	version = "1.0" 
	encoding = "UTF-8" 
	standalone = "no" 
?>

<!DOCTYPE address SYSTEM "address.dtd">

<address>


  <name>Tom Peters</name>

  <company>Fidelity Investments</company>

  <phone>710-181-1910</phone>

  <industry>
    Finance  
  </industry>
  
</address>

 

Output

Textual

The element ‘address’ has invalid child element ‘industry’.

Image

 

Explanation

Our editor thankfully informed us that the address element is not one of the allowed child elements availed under address.

 

DTD External – Adding new Element – Finance – Commented Out Using <!– and –>

Outline

We will comment out the industry tag.

address.dtd

<!ELEMENT address (name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>

sample.dtd.external.element.added.finance.xml

<?xml 
	version = "1.0" 
	encoding = "UTF-8" 
	standalone = "no" 
?>

<!DOCTYPE address SYSTEM "address.dtd">

<address>


  <name>Tom Peters</name>

  <company>Fidelity Investments</company>

  <phone>710-181-1910</phone>

  <!--
  
    <industry>
      Finance  
    </industry>
  
  -->
  
</address>

 

 

DTD External – Adding new Element – Finance – Commented Out Using Nested Comments

Outline

We will complicate our pathway by attempting to use nested comments.

address.dtd

<!ELEMENT address (name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>

sample.dtd.external.element.added.finance.commented.nested.xml

<?xml 
	version = "1.0" 
	encoding = "UTF-8" 
	standalone = "no" 
?>

<!DOCTYPE address SYSTEM "address.dtd">

<address>


  <name>Tom Peters</name>

  <company>Fidelity Investments</company>

  <phone>710-181-1910</phone>

  <!--
  
    <!--
      <industry>
        Finance  
      </industry>
    
    -->
    
  -->
  
</address>

Output

Textual

Character sequence ‘–‘ is illegal inside XML comments.

Image

 

Explanation

The XML parser tripped on nested comments.

 

DTD External – Adding new Element – Finance – Commented Out Using ‘Unused Processing Instruction’

Outline

Unused processing instruction allows more complex processing.

address.dtd

<!ELEMENT address (name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>

sample.dtd.external.element.added.finance.commented.unusedProcessingInstruction.xml

<?xml 
	version = "1.0" 
	encoding = "UTF-8" 
	standalone = "no" 
?>

<!DOCTYPE address SYSTEM "address.dtd">

<address>

  <name>Tom Peters</name>

  <company>Fidelity Investments</company>

  <phone>710-181-1910</phone>

  <!--
    Surround the section with an unused processing instruction
    Starting the comment with <?comment
  -->
  <?comment
    <!--
      <!--
        <industry>
          Finance  
        </industry>
      -->
    -->
  ?>
  <!--
    Surrounded the section with an unused processing instruction
    Ending the comment with ?>
  -->

</address>

Commending

The Impaler

Big gratitude to “The Impaler”.

Link

Image

Text

You shouldn’t do it, I know. Per the XML specification you aren’t supposed to.

Having said that… I really needed it badly, so here’s the trick. Surround the section you want to comment with an unused processing instruction:

<some-tags />

<?comment
<!– traditional comment 1 –>
<badtag prop1=”123″>
<!– traditional comment 2 –>
</badtag>
<!– traditional comment 3 –>
?>

<rest-of-my-tags />
You can use any processing instruction that’s not in use. I chose “comment” as the unused processing instruction, so I started the big comment with <?comment and ended it with ?>.

Pretty much any word will do as a processing instruction since they aren’t really used most of the time. I mean, when was the last time you used one?

 

Environment

Unfortunately, the plugin that I am using with Notepad++ failed me miserably.

Thankfully, Microsoft’s Visual Studio bailed me out.

 

Source Code

GitHub

DanielAdeniji/XMLComment

Link