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   When Emacs Lisp attempts to evaluate a form that, for some reason,
cannot be evaluated, it "signals" an "error".

   When an error is signaled, Emacs's default reaction is to print an
error message and terminate execution of the current command.  This is
the right thing to do in most cases, such as if you type `C-f' at the
end of the buffer.

   In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers which should be deleted before
the program is finished.  In such cases, you would use `unwind-protect'
to establish "cleanup expressions" to be evaluated in case of error.
Occasionally, you may wish the program to continue execution despite an
error in a subroutine.  In these cases, you would use `condition-case'
to establish "error handlers" to recover control in case of error.

   Resist the temptation to use error handling to transfer control from
one part of the program to another; use `catch' and `throw'.  *Note
Catch and Throw::.

* Signaling Errors
How to report an error.
* Processing of Errors
What Emacs does when you report an error.
* Handling Errors
How you can trap errors and continue execution.
* Error Names
How errors are classified for trapping them.

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