Doc should clarify Path requirements for PathObserver, Path

[arthurevans]

e.g., '0' is not a valid path, but '[0]' is.

See Polymer/polymer#526

[tachyon1337]

Full agreement. There are some that use the Platform but not polymer itself. This undocumented "valid path" change caused a wtf evening of frustration when switched over to the newest version, a switch in large part prompted by Observe being released to Chrome stable. Not sure why backwards compatibility was not retained.

To clarify with an example: whereas before you could do this:

new PathObserver($scope,'profile.0.name')

getPath in the constructor will now return the path as invalid. So you now have to do something like this:

new PathObserver($scope,'profile[0].name')

[jmesserly]

I think this is a dupe of #6