It's pedantic, but it's a tad clunky now: I'd use something like "wow/such/deep[3]/much/power/!" to differentiate child nodes from array indexes, and also strongly advise against a node named "!" on principle. Of course then you'd say "but I want '/' in my node name!", and then you get to bikeshed an escape sequence, but you'd need that anyway for a node name with '[' or ']' in it.
However, what they've done is workable if all the browser vendors implement it.
square brackets are a reasonably common way to access data in an hash-like object. both Javascript (objects) and PHP (associative arrays) use/allow square brackets for this.
However, what they've done is workable if all the browser vendors implement it.