Charlie Holland has a very nice contribution to June’s Emacs Carnival about underappreciated Emacs builtins. His post is about the Emacs help system and how you can use it to learn everything about Emacs. It’s a commonplace to say that Emacs is self-documenting but that’s little more than a slogan. Holland takes a long look at what that actually means.
He begins by noting that the help system is self-recursive is the sense that you can ask the help system about the help system. You simply call the help-for-help command intuitively bound to Ctrl+h Ctrl+h. If you’ve never tried it, try it now. It gives you a nice listing of every help command.
Once you invoke help for a certain command or variable, you get a buffer containing a description of the command or variable as well as links to related commands/variables and the source code of the command so you can see exactly what it does and how it does it. You can discover what command a shortcut calls or what the shortcut for a command is with a simple help call.
There are a bunch of other aspects to the help system. You can, for example, get a listing of what your last commands were, complete information about the character at point, the current value of a variable, the current mode, and lots more.
For discovery, there are the apropos command and its siblings to help you find what you’re looking for even if you have no idea of its name. You merely need to have a general description of what it does. Fuzzy completion on command invocation (Meta+x) helps you find the right command even if you have only a vague idea of its name.
Hoplland’s post is long and has a lot of information but it’s one that every Emacs n00b—or more experienced user, for that matter—should read. In Holland’s terminology, it’s the first node in the Emacs knowledge graph.