Up to the R5RS standard, the standard comment in Scheme was a semicolon, which makes the rest of the line invisible to Scheme. Numerous implementations have supported alternative conventions permitting comments to extend for more than a single line, and the R6RS standard permits two of them: an entire s-expression may be turned into a comment (or "commented out") by preceding it with codice_90 (introduced in SRFI 62) and a multiline comment or "block comment" may be produced by surrounding text with codice_91 and codice_92.