I own the classic tome by R. O Gray and C.J Corbally – ‘Stellar Spectral Classification’ and it contains a wealth of material ordered using (mainly) the regular spectral classes. I doubt there is much I will ever need to know that is not in there…
However, I recently stumbled across the following web-page
https://ned.ipac.caltech.edu/level5/Gray/frames.html
which appears to be a very early version of the text, or more properly, some brief notes which were its foundation…
It is presented as a series of single, short pages, each of which is a ‘vignette’ on a particular focussed topic. The text is short (single paragraph) and each page has a single image of spectra. The brevity may be due, in part, to the early web-page technology that appears to underly it. I find this approach much more accessible, and each page could be the foundation for a small observation project…
There is another page at
http://spectra.astro.uni.wroc.pl/elements/dsa3.pdf
which shows evolution towards the main book, but which is also quite short (and is in pdf form)