We all have heard of "fastboot boot xxxx" command. How does it work when you use it for kernel (fastboot boot boot.img)? Is it simple as this: it boot Android with that kernel if possible or it make that kernel permanent, if not how does it work? Does it just put kernel you specified in RAM instead of one in internal memory? Also what happens if kernel can't boot for some reason does it soft-brick device or just boot existing kernel? And if kernel is ok and it boot how to get back to using kernel from inernal memory?