9.1.3.1.2 Leading and Trailing Newlines in Condition Reports

It is recommended that a report message not begin with any introductory text, such as ``Error: '' or ``Warning: '' or even just freshline or newline. Such text is added, if appropriate to the context, by the routine invoking the condition reporter.

It is recommended that a report message not be followed by a trailing freshline or newline. Such text is added, if appropriate to the context, by the routine invoking the condition reporter.

 (error "This is a message.~%")   ; Not recommended
 (error "~&This is a message.")   ; Not recommended
 (error "~&This is a message.~%") ; Not recommended

 (error "This is a message.")     ; Recommended instead