Plain TeX provides the \tracingall command, to turn on the
maximum amount of tracing possible in TeX. The (usually voluminous)
output from \tracingall goes both on the terminal and into the
transcript file.
It is sometimes easier to have the output go only to the transcript
file, so you can peruse it at your leisure and not obscure other output
to the terminal. So, Eplain provides the command \loggingall.
(For some reason, this command is available in Metafont, but not in
TeX.)
It is also sometimes useful to see the complete contents of boxes.
\tracingboxes does this. (It doesn't affect whether or not the
contents
are shown on the terminal.)
You can turn off all tracing with \tracingoff.
You can also turn logging on and off globally, so you don't have to
worry about whether or not you're inside a group at the time of command.
These variants are named \gloggingall
and \gtracingall.
Finally, if you write your own help messages (see \newhelp
in The TeXbook), you want a convenient way to break lines in
them. This is what TeX's \newlinechar parameter is for;
however, plain TeX doesn't set \newlinechar. Therefore,
Eplain defines it to be the character ^^J.
For example, one of Eplain's own error messages is defined as follows:
\newhelp\envhelp{Perhaps you forgot to end the previous^^J%
environment? I'm finishing off the current group,^^J%
hoping that will fix it.}%