Comments that begin with a single semicolon are all aligned to the same column at the right (sometimes called the “comment column”). The text of such a comment generally applies only to the line on which it appears. Occasionally two or three contain a single sentence together; this is sometimes indicated by indenting all but the first with an additional space (after the semicolon).
2.4.4.2.2 Use of Double Semicolon
Comments that begin with a double semicolon are all aligned to the same level of indentation as a form would be at that same position in the code. The text of such a comment usually describes the state of the program at the point where the comment occurs, the code which follows the comment, or both.
2.4.4.2.3 Use of Triple Semicolon
Comments that begin with a triple semicolon are all aligned to the left margin. Usually they are used prior to a definition or set of definitions, rather than within a definition.
2.4.4.2.4 Use of Quadruple Semicolon
Comments that begin with a quadruple semicolon are all aligned to the left margin, and generally contain only a short piece of text that serve as a title for the code which follows, and might be used in the header or footer of a program that prepares code for presentation as a hardcopy document.
Not exactly. ;; aligns to the current indentation level of the code.
It's a usual Lisp indenting convention.
The Emacs Lisp manual recommends:
https://www.gnu.org/software/emacs/manual/html_node/elisp/Co...
Common Lisp uses it also. See the ANSI CL spec.
2.4.4.2.1 Use of Single Semicolon
Comments that begin with a single semicolon are all aligned to the same column at the right (sometimes called the “comment column”). The text of such a comment generally applies only to the line on which it appears. Occasionally two or three contain a single sentence together; this is sometimes indicated by indenting all but the first with an additional space (after the semicolon).
2.4.4.2.2 Use of Double Semicolon
Comments that begin with a double semicolon are all aligned to the same level of indentation as a form would be at that same position in the code. The text of such a comment usually describes the state of the program at the point where the comment occurs, the code which follows the comment, or both.
2.4.4.2.3 Use of Triple Semicolon
Comments that begin with a triple semicolon are all aligned to the left margin. Usually they are used prior to a definition or set of definitions, rather than within a definition.
2.4.4.2.4 Use of Quadruple Semicolon
Comments that begin with a quadruple semicolon are all aligned to the left margin, and generally contain only a short piece of text that serve as a title for the code which follows, and might be used in the header or footer of a program that prepares code for presentation as a hardcopy document.