XML versus Unicode ... here are the facts about their differences

["Costello, Roger L." <costello@mitre.org>]

Hi Folks,

Below I have listed the differences between XML and Unicode as explicitly and completely as I can. Please let me know where I err.

Assume: This XML tag uses the precomposed ñ character:

	<Martiñez>

Assume: This XML tag uses 'n' plus the "combining tilde" character:

	<Martiñez>

Fact: The two tags are visually IDENTICAL. More precisely, the glyphs on display screens are IDENTICAL.

Fact: Below are two representations of the SAME CHARACTER:

	a. precomposed ñ character

	b. 'n' plus the "combining tilde" character 

Fact: According to the Unicode standard, the two representations ARE EQUIVALENT.

Fact: According to the XML standard, the two representations ARE NOT EQUIVALENT.

Fact: According to the Unicode standard, applications must treat the two representations exactly the SAME. Applications must compare the two representations as EQUAL.

Fact: According to the XML standard, applications must treat the two representations as DIFFERENT. XML applications must compare the two representations as NOT EQUAL.

Fact: In XML two Unicode-identical CHARACTERS may be considered to be DIFFERENT.

Fact: XML parsing is done on codepoints, not characters nor on the bytes that are used inside the computer to represent the codepoints.

Fact: XML parsing is done on codepoints, but XPath does NOT do its string matching operations based on codepoints. XPath uses a byte-for-byte comparison.

What "Facts" are not correct?

/Roger

[1] The precomposed ñ character and the 'n' plus the "combining tilde" character are equivalent: see the book, "Unicode Demystified" page 119.