need to expose QML console documentation better

We use console.log all over QML examples and snippets, but searching for "console" in the help index finds nothing. Only the Creator syntax completion will tell you that console.warn, console.error etc. also exist. (Or, generic JS documentation elsewhere on the web)

It would also be nice to know where and what is the console object, how to redirect it, how to enable/disable output on various platforms, etc.

But it may change if we implement it in the JS engine instead of only in QML.