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

406 Appendix C. Error Messages
The response H 〈return〉 at this point leads to the same message as
for the first error. A correction with an I entry will not do any good since
the missing \begin{quote} can no longer be inserted ahead of the environment
text. Entering I\begin{quote} will replace the \end{quote}
with \begin{quote}, but that does not solve the real problem. The best
response now is to type 〈return〉 so that the command \end{quote} is
ignored and the processing continues.
Now both the faulty \begin{qoute} and correct \end{quote} commands
are removed and the processing takes place as if the quote environment
had never been in the input text at this point.
If the typing error qoute had been made in the \end instead of in the
\begin command, the error message would have been:
! LaTeX Error: \begin{quote} on input line 3 ended by \end{qoute}
See the LaTeX manual or LaTeX Companion for explanation.
Type H for immediate help.
...
l.5 \end{qoute}
?
The previous explanations should be enough for the user to understand
what is now being said. The error indicator here is
\begin{quote} on input line 3 ended by \end{qoute}
and the last pair of lines indicate that the problem is in line 5 and that the
troublesome command is \end{qoute}. The obvious thing to do now, and
the H message encourages this conclusion, is to make a correction with
I\end{quote}. However, now a new message appears on the monitor:
! Extra \endgroup.
\endgroup
l.5 \end{qoute}
?
With the exception of the last pair beginning with l.5, this makes no
sense at all. The error indicator ! Extra \endgroup is seemingly meaningless.
That this is a T E X error message and not a L AT E X one is hardly any
compensation.
The frustrated user is not really to blame. The response was perfectly
reasonable even if it was wrong. Only experience could say that the
best action at that point was to have just pressed 〈return〉. The quote
environment is closed off anyway, although any special actions associated
with \end{quote} would be left off.
The help message at this point is