9.1.3.1.1 Capitalization and Punctuation in Condition Reports

It is recommended that a report message be a complete sentences, in the proper case and correctly punctuated. In English, for example, this means the first letter should be uppercase, and there should be a trailing period.

 (error "This is a message")  ; Not recommended
 (error "this is a message.") ; Not recommended

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