Because its siblings are incremental from zero, They are arrays, if not they are hash.It can be no ambiguity and iterateable, if key is 0, It see himself as an array to expect 1 2 and so on.
that's rare, I'm not meant to make it a new all rounded config format, But with '0' ,it is interpreted as string key. It will not deal multi line or escaped something. Just notice single quote mark and content should never contain single quote mark.Or just never contain any space, get the parse to array and hash ref right first.