Question: Non-projected vectors: Is this a Maple term (and related questions)?

I'm trying to get familiar with the Physics package. It's huge.  Since I know vector projection, I can guess what a projected vector might be. But what would a non-projected vector be in a physical context? 

A web search for non-projected vectors was unsuccessful.

My best guess is that non-projected vectors in Maple are those where no coordinate system is specified for vectors in an expression for a physical law. Like here in Maxwell equations. Am I correct?

To distinguish between these vectors the Physics[Vector] package uses an underscore “_”.

If my understanding is correct so far, I have three questions:

• Can I replace the unit vectors of implemented projected vectors to something else (e.g. _i to e__x)
• Is it possible to define projected vectors beyond what is implemented in Maple?
• Can I use the packages VectorCalculus and Physics[Vector] at the same time?