Info Catalog
elisp: Printing Notation
elisp: Conventions
elisp: Buffer Text Notation
1.3.5 Error Messages
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Some examples signal errors. This normally displays an error message in
the echo area. We show the error message on a line starting with
‘error→’. Note that ‘error→’ itself does not appear in the echo area.
(+ 23 'x)
error→ Wrong type argument: number-or-marker-p, x