A comment starts with two adjacent hyphens and extends up to the end of the line. A comment can appear on any line of a program. The presence or absence of comments has no influence on whether a program is legal or illegal. Furthermore, comments do not influence the effect of a program; their sole purpose is the enlightenment of the human reader.
-- the last sentence above echoes the Algol 68 report end; -- processing of LINE is complete -- a long comment may be split onto -- two or more consecutive lines ---------------- the first two hyphens start the comment
Horizontal tabulation can be used in comments, after the double hyphen, and is equivalent to one or more spaces (see 2.2).
References: end of a line, illegal, legal, space character.
Rationale references: 2.1 Lexical Structure
Style Guide references: 2.1.4 Alignment of Declarations, 2.1.7 Pagination, 3.3 Comments, 5.2.1 Formal Parameters, 5.6.7 Goto Statements, 5.6.8 Return Statements, 7.1.3 Comments, 7.1.5 Encapsulating Implementation Dependencies, 7.2.5 Comments, 8.3.5 Iterators
Address any questions or comments to firstname.lastname@example.org.