What’s the difference between Rock & Roll and Country/Western music?

[Thudlow_Boink]

I found this older thread:

What's the difference between Country and Rock?

Is there any bright-line test? The Rolling Stones have written and performed country songs. Toby Keith has been known to rock out on occassion. Where do you draw the line? Especially since country is one of the roots of rock. Is it the presence of a slide guitar? Does a pickup truck have to be involved somewhere? Is the Marshall Tucker Band one or the other?