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The pure essence of XML: these are the acceptable strings

• From: "Costello, Roger L." <costello@mitre.org>
• To: "xml-dev@lists.xml.org" <xml-dev@lists.xml.org>
• Date: Mon, 25 Nov 2013 11:50:28 +0000

Hi Folks,

If we strip away all the syntax, what it all boils down to is this:

	Is this string of characters
	acceptable?

We want our XML documents to contain acceptable strings, and we want to reject all others.

That is what XML is all about, at its pure essence. 

Consider this XML:

	<A B="b">a</A>

Let's suppose that the only acceptable value for <A> is the character 'a' and the only acceptable value for @B is the character 'b'.

So what are the acceptable strings? Is it:

	1. ab
	2. ba
	3. ab and ba

If you were to write a grammar to define the acceptable strings, how would you write it? Like this:

	A --> Ba
	B --> b

Or like this:

	A --> aB
	B --> b

Or perhaps like this:

	A --> aB | Ba
	B --> b

If you were to rewrite the XML using elements only, would you write it like this:

	<A><B>b</B>a</A>

Or like this:

	<A>a<B>b</B></A>

/Roger