Core Module Documentation Content Missing??

I’ve been trying to get some information/instructions on using a core module, the book module in particular ( and I’m not seeing any of what I would consider the body content in the page display.  It seems to be virtually the same for all the core module documentation. I’m pretty sure I was able to view the information earlier in the week.  I’ve tried both Firefox and Chrome and both display pretty much the same page.  Am I looking in the wrong place for detailed documentation?  Thank you, in advance, for your assistance.

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