[tannhaeuser]

That's because originally SGML/HTML/XML attributes were for (mostly) presentational details, but this role was shifted to CSS. The resulting combination does indeed look arbitrary, especially with CSS's total lack of mental discipline (but let's not be too harsh here).

In judging whether something should be represented as element text or as attribute, ask yourself whether that something is content or metadata. In a context where this distinction doesn't make sense, markup (SGML, XML, HTML) probably doesn't make sense either.

Markup isn't and never was intended for representing arbitrary data - it is for representing text with optional markup, and is designed for end-users and content authors, not necessarily web developers.

As for representing XML in code, there was E4X which allowed you to represent XML literals in Javascript (Firefox and rhino had it a couple years ago, but it kindof wasn't convincing). Keep in mind that Javascript was invented as a language to manipulate a DOM in the first place, so there you have your canonical representation of markup in Javascript.

[tannhaeuser]

Looking at the other comments, I realize you're looking for object/XML mapping. My opinion is that this is pointless (and I'm guilty of applying it back in the SOAP days, too), because objects are co-inductive data structures based on the types of programming languages, whereas XML is based on grammars eg. a description of a class of sequences of content tokens.

Sure you can represent objects, ie. a memory dump of a running program, as XML, but what's the point?

[tracker1]

If it doesn't map cleanly to a program representation in some way, then what is the point, when it's harder to do real work with?