People all too often forget that there is often a lot of extra documentation hidden in /usr/share/doc/ when you install -doc packages, at least on deb systems, and not just info and manpages. For example, the bash manual you cite is in /usr/share/doc/bash/bashref.pdf along with its html version as bashref.html. There is also an /example/ folder filled with commented programs and functions to serve as reference. And a README that suggests looking for "Advanced Bash-Scripting Guide" which is a massive online book filled with all sorts of esoteric knowledge. You can also find things like the release changelogs and one that details incompatibilities from previous versions.

While there are exceptions, most packages have useful goodies in there to check first before one has to think about looking things up online.