The Utility of In-Depth Tutorial?

some tutorials, rare, goes into excruciating detail. Such as the JavaScript Book by David Flanagan (rhino) [see JavaScript Book by David Flanagan, and Man-made Complexity in Computer Language]

but, i wonder the utility. For the 0.1% who need to know, you probably shouldn't (because you are probably abusing the language). And for the rest, testing code out yourself is more practical and reliable than book.

(am wondering because my JavaScript tutorial JavaScript in Depth is in depth, and now teetering on being esoteric, wonder if i should curtail in that direction. (and consider the “http://www.w3schools.com/”, which is the most popular js tutorial by far, is simplistic to actually being incorrect often. (similarly, lots commercial programing tutorials are borderline wrong simplistic. (but part of the reason they are popular is because they are for beginners.))))

when you need to know some painful detail of a lang not covered by basic tutorial, you are on the verge of abusing the lang. Question your need/approach.

well, in depth tutorial is actually still useful, because the spec may be hard to read or doesn't exist. And, for many things, it may be hard to test to find out.