The PAT LessCSS code convention.I'm building a command line that checks and sometimes even fixes code convention violations: https://github.com/WouterBos/Peruse

LessCssConvention.css

/**
 * Each file should begin with a document comment, describing what it should do
 */






/**
 * Brace styles, nesting and naming.
 */
/* Always prefix a root class with some namespace. In this case it's "prfx_" */
/* Also: always start a nested rule with a comment stating its purpose. */
/* In BEM terminology this is Block. */
.prfx_blockName {
	/* Child classes should be prefixed with the name of the root class. In this case: "prfx_blockName". */
	/* In BEM terminology this is Element. */
	.prfx_blockName_nestedItem {
		/* Each selector starts on a new line. */
		&,
		&:hover,
		&:link,
		&:visited,
		&:focus {
			.item {
				/* WRONG: Prevent nested selectors if the parent selector is long or has many commas. */
			}
		}
	}

	/* Additional block styling is always recognizable through use, thus do not need a different notation. */
	/* In BEM terminology this is Modifier. */
	&.prfx_blockName__modifier {
		/* Element style connected to Modifier. */
		.prfx_blockName_nestedItem {
		}
	}
}

/* Large blocks can have modifiers written like this: */
.prfx_blockName.prfx_blockName__modifier {
}



/**
 * Property order
 *
 * Properties are ordered in sections. The sections are ordered outside-in. You start with the
 * outer styling of the box and end with the inner content and properties like shadow. Variables
 * are always first, because it has to be clear what variables are used. Second are references
 * to mixins, since they might hold different types of properties and because they might have to
 * be overruled.
 */
.prfx_someOtherBlockName {
	/* Variables, followed by a blank line */
	@foo: 1px;

	/* References to mixins */
	.transform(rotate(7deg));
	/* Page properties */
	marks: value;
	orphans: value;
	page: value;
	page-break-after: value;
	page-break-before: value;
	page-break-inside: value;
	size: value;
	widows: value;
	/* Box properties */
	clear: value;
	clip-path: value;
	cursor: value;
	display: value;
	float: value;
	opacity: value;
	visibility: value;
	/* Table properties */
	table-layout: value;
	caption-side: value;
	border-collapse: value;
	border-spacing: value;
	empty-cells: value;
	/* Positioning */
	position: value;
	top: value;
	right: value;
	bottom: value;
	left: value;
	z-index: value;
	/* Margin */
	margin: value;
	margin-top: value;
	margin-right: value;
	margin-bottom: value;
	margin-left: value;
	/* Border */
	outline: value;
	outline-color: value;
	outline-style: value;
	outline-width: value;
	border: value;
	border-top: value;
	border-right: value;
	border-bottom: value;
	border-left: value;
	border-width: value;
	border-top-width: value;
	border-right-width: value;
	border-bottom-width: value;
	border-left-width: value;
	border-style: value;
	border-top-style: value;
	border-right-style: value;
	border-bottom-style: value;
	border-left-style: value;
	border-color: value;
	border-top-color: value;
	border-right-color: value;
	border-bottom-color: value;
	border-left-color: value;
	/* Padding */
	padding: value;
	padding-top: value;
	padding-right: value;
	padding-bottom: value;
	padding-left: value;
	/* Dimensions */
	width: value;
	max-width: value;
	min-width: value;
	height: value;
	max-height: value;
	min-height: value;
	/* Content box behaviour */
	overflow: value;
	white-space: value;
	/* List styles */
	list-style: value;
	list-style-image: value;
	list-style-position: value;
	list-style-type: value;
	/* Generated content */
	content: value;
	counter-increment: value;
	counter-reset: value;
	quotes: value;
	marker-offset: value;
	/* Text styling */
	color: value;
	direction: value;
	font: value;
	font-family: value;
	font-size: value;
	font-size-adjust: value;
	font-stretch: value;
	font-style: value;
	font-variant: value;
	font-weight: value;
	letter-spacing: value;
	text-align: value;
	line-height: value;
	text-decoration: value;
	text-indent: value;
	text-shadow: value;
	text-transform: value;
	unicode-bidi: value;
	vertical-align: value;
	word-spacing: value;
	/* Speech */
	azimuth: value;
	cue: value;
	cue-after: value;
	cue-before: value;
	elevation: value;
	pause: value;
	pause-after: value;
	pause-before: value;
	pitch: value;
	pitch-range: value;
	play-during: value;
	richness: value;
	speak: value;
	speak-header: value;
	speak-numeral: value;
	speak-punctuation: value;
	speech-rate: value;
	stress: value;
	voice-family: value;
	volume: value;
	/* Background */
	background: value;
	background-attachment: value;
	background-color: value;
	background-image: value;
	background-position: value;
	background-repeat: value;
	box-shadow: value;
}



/**
 * Browser vendors
 *
 * Always move repeating code like properties with browser prefixes to a seperate
 * (parametric) mixin.
 */
.prfx_transform(@value: ~"") { /* Always define default values for mixins */
	transform: @value;
	-ms-transform: @value;
	-moz-transform: @value;
	-webkit-transform: @value;
	-o-transform: @value;
}



/**
 * Modules
 *
 * Always make logical blocks of files, which can be imported through one central file.
 */

/* Base */
@import "prfx_values.less";
@import "prfx_functions.less";
@import "prfx_reset.less";

/* Text styling */
@import "prfx_text.less";
@import "prfx_text-block.less";

/* Grid */
@import "prfx_grid.less";
@import "prfx_grid-print.less";
@import "prfx_grid-mobile.less";
@import "prfx_grid-flex.less";




/**
 * Misc
 *
 * - Indentions as 4 spaces (if Less code will never be parsed in-browser).
 *      Spaces will show the intended indention.
 * - Always add a space after a colon.
 * - Maximum depth of mixins: 5.
 *      Complex selectors take up space and take a longer time to render. Aim for a flat structure.
 * - Maximum line width of comments: 120 characters.
 *      So that all code can be read without horizontal scrolling. This restriction is only imposed on comments,
 *	since CSS styling itself rarely exceeds the 120 char restriction.
 * - Never use an ID as a selector
 *      ID selectors make a style hard to reuse because an ID needs to be unique in the code. Furthermore:
 *	ID selectors are too strong and serve as a pseudo-!important.
 * - A line never ends with a space.
 */