[tex-eplain] Thank you Laurence for glyph_test example; eplain won't load compatible packages

[Karl Berry]

    Hello Mr. Berry,

Please call me Karl.

    ! Undefined control sequence.
    l.103 \protected

In short: run etex, not tex.

Longer explanations:

1. I can't reproduce that error. Please send runnable examples when
possible. For me, running tex on
\input miniltx
\input graphicx
works fine.

However, running tex on
\input eplain
\beginpackages
\usepackage{graphicx}
\endpackages
\end
I get an error about \detokenize:
! Undefined control sequence.
l.173 \edef\Gin at gzext{\detokenize

2. Some years ago, LaTeX started requiring a few primitives that are not
part of Knuth's TeX. Skipping over details, \protected and \detokenize
are two of those. If you run your document with etex (dvi output) or
pdftex (pdf output), you'll have them.

3. Indeed, the colors around link borders are not related to the color
package, as I recall.

4. I agree with Laurence's general summary that the basic idea of LaTeX
and plain TeX are not compatible, and very different.

I don't know if it would interest anyone, but a new format optex has
been developed recently (by Petr Olsak). He attempted to provide the
same sort of basic user-level ideas as LaTeX (sectioning, decent font
support, and so on; much much more than Eplain), but it can be
customized and changed using plain TeX macros, not requiring learning a
more-or-less new macro world as LaTeX does. It's also based on LuaTeX,
which opens many doors.  It's an impressive piece of work, IMHO.
https://ctan.org/pkg/optex

All the best,
Karl

P.S. You can leave out the asterisks around package names, etc.
They're just a distraction :).

P.P.S. Regarding books, I certainly second Laurence's recommendation of
The TeXbook. But not everyone does well with Knuth's unique style of
writing. Two more "normal" books about plain TeX are available at no
cost, and are part of TeX Live: TeX by Topic (by Victor Eijkhout) and
TeX for the Impatient (by Paul Abrahams, Kathy Hargreaves, and me). 
https://ctan.org/pkg/texbytopic
https://ctan.org/pkg/impatient

TbT, in particular, is clearly written (IMHO) reference manual. I like
it better than our book :).