[json] JSON Naming Convention (snake_case, camelCase or PascalCase)

Is there a standard on JSON naming?
I see most examples using all lower case separated by underscore, aka snake_case, but can it be used PascalCase or camelCase as well?

In this document Google JSON Style Guide (recommendations for building JSON APIs at Google),

It recommends that:

1. Property names must be camelCased, ASCII strings.

2. The first character must be a letter, an underscore (_) or a dollar sign ($).

Example:

{
  "thisPropertyIsAnIdentifier": "identifier value"
}

My team follows this convention.