Guide to LaTeX (4th Edition) (Tools and Techniques

404 Appendix C. Error Messages
problem. Following are one or more lines of input text. The last symbol
of the first of these lines is the one that has caused T E X to stop and print
the error message. The last line contains the text or commands that are
the next to be processed. T E X waits for a response from the user. If
that response is the typing of an H for help, a more detailed description,
with possible tips, is printed to the monitor, and T E X waits for a further
response.
C.1.2 L AT E X error messages
As an example of a text with a L AT E X error, we take
\documentclass{article}
\begin{document}
\begin{qoute}\slshape
Text indented at both ends
\end{quote}
\end{document}
Here the call \begin{quote} was incorrectly typed as qoute. The L AT E X
processing writes the error message:
! LaTeX Error: Environment qoute undefined.
See the LaTeX manual or LaTeX Companion for explanation.
Type H for immediate help.
...
l.3 \begin{qoute}
\slshape
?
The first line of this message states that L AT E X itself discovered this error,
with a brief error indicator, in this case Environment qoute undefined.
All L AT E X error messages begin with a line like this, followed by a reference
to the L AT E X manuals for detailed explanation (which is also to be found
in Section C.3 of this book). The third line of text is a reminder that the
response H 〈return〉 will also type additional clarification.
The line of three dots ... indicates that there are more lines of internal
! coding that have been suppressed. Sometimes it is desirable to look deeper
behind the error message, especially for practiced T E Xperts who know how to
interpret them. In this case, L AT E X can be made to output the missing lines of
coding by setting
\setcounter{errorcontextlines}{num}
where num is the number of levels a macro will be decoded on an error. By
default, num = −1. The knowledgeable user can set it to 99 to get more lines
than he or she will ever likely to want.