I am a non-beginner plain TeX user, mostly typesetting cheat sheets for computer science. I own The TeXbook and have seen some TeX manuals for the compilers, such as pdfTeX manuals and so forth.
My problem is that I struggle to find online information whenever I want to find out more about some macro that is not working, or some specific fine point of TeX typesetting. (For example today, I needed to learn more about
\fam and how to typeset bold fonts in math mode, and it took me a while before I learned which commands to use and how.)
The major problem with searching for plain TeX information is that 90% of information I find through Google search are relevant to LaTeX and not plain.
Are there any good online documents/websites in English that describe in detail finer points on plain TeX? List built-in macros, recommended practices (many people define their own variation on optional variables in macros), and so on?
As an example of literature that I look for, I have found TeXbook naruby, which is a book in Czech about TeX and lists its base macros with examples and explanations. I would like to find comparable literature/website in English for plain TeX.