What is Custom XML?

Consider HTML. It has a well-defined set of tags (such as <i> and <b> and so on). If somebody were to write a software package that allowed for additional tags, then such additional tags could be construed as "custom" tags. XML, however, doesn't have a pre-defined set of tags. You can use any tags you want, and it's up to the software you're using (or creating) to handle the tags appropriately. Some people have argued that as such, all XML is "custom" and therefore the phrase in the judge's ruling-custom XML-is redundant at best, ridiculous at worst.

But there are two more possibilities for what it means. Microsoft's MSDN documentation and the Open XML specification both talk about Custom XML in two separate ways. First, there's an XML tag called customXML whereby you, the tech-savvy user, can embed your own XML in a Word document that goes beyond the XML already used by Word. To do this, you use a part of the Word GUI that you can get to through the Developer tool bar on the ribbon in the XML tab. (I found this article online that describes it pretty well.)

The next possibility is how you can include your own XML files right inside the single .zip file making up an Open XML document. Within the MSDN documentation, this is called Custom XML.

So we have three possibilities-the first being a simple redundancy (or absurdity); the second being the customXML tags for attaching XML codes to your text; and the third being Custom XML for adding XML files into the .zip files.

To help figure out which type the judge meant, I found this document, titled "Memorandum Opinion and Order," signed by the judge. (You can find other documents pertaining to the case here.) The document contains many mentions of "custom XML" (and even includes a footnote about whether or not the term is defined elsewhere, even though the document doesn't actually define the term). The document is filled with mentions of custom XML, such as this:

"Microsoft argues that ... custom XML functionality is simply a small part of ... Word ..."

But there's this gem, which provides the biggest clue:

"adding custom XML elements using the XML structure pane of WORD's graphical user interface"

The part about the XML structure pane in Word pretty much tells the story. It is my opinion that the "custom XML" refers to the second possibility, that of new XML tags that can be manipulated from the XML tab of the Developer tool bar. On that tab is a button called Structure, which opens a pane called XML Structure-just what the Memorandum refers to. This is apparently the "custom XML" that the judge was referring to in the permanent injunction.