less.js

Allow comments in keyframe (complete comment support coming in 2.0)
pass options to parser from less.render
Support /deep/ combinator
handle fragments in data-uri's
float @charsets to the top correctly
updates to some dependencies
Fix interpolated import in media query
A few other various small corrections

Handle uppercase paths in browser
Show error if an empty selector is used in extend
Fix property merging in directives
Fix ordering of charset and import directives
Fix race condition that caused a rules is undefined error sometimes if you had a complex import strategy
Better error message for imports missing semi-colons or malformed
Do not use util.print to avoid deprecate warnings in node 0.11

Include dist files, missing from 1.7.2
Do not round the results of color functions, like lightness, hue, luma etc.
Support cover and contain keywords in background definitions

Allow paths option to be a string (in 1.7.1 less started throwing an exception instead of incorrectly processing the string as an array of chars)
Do not round numbers when used with javascript (introduced 1.7.0)

Fix detection of recursive mixins
Fix the paths option for later versions of node (0.10+)
Fix paths joining bug
Fix a number precision issue on some versions of node
Fix an IE8 issue with importing css files
Fix IE11 detection for xhr requests
Modify var works if the last line of a less file is a comment.
Better detection of valid hex colour codes
Some stability fixes to support a low number of available file handles
Support comparing values with different quote types e.g. "test" now === 'test'
Give better error messages if accessing a url that returns a non 200 status code
Fix the e() function when passed empty string
Several minor bug fixes

Add support for rulesets in variables and passed to mixins to allow wrapping
Change luma to follow the w3c spec, luma is available as luminance. Contrast still uses luma so you may see differences if your threshold % is close to the existing calculated luma.
Upgraded clean css which means the --selectors-merge-mode is now renamed --compatibility
Add support for using variables with @keyframes, @namespace, @charset
Support property merging with +_ when spaces are needed and keep + for comma separated
Imports now always import once consistently - a race condition meant previously certain configurations would lead to a different ordering of files
Fix support for .mixin(@args...) when called with no args (e.g. .mixin();)
Do unit conversions with min and max functions. Don't pass through if not understood, throw an error
Allow % to be passed on its own to the unit function e.g. unit(10, %)
Fix a bug when comparing a unit value to a non-unit value if the unit-value was the multiple of another unit (e.g. cm, mm, deg etc.)
Fix mixins with media queries in import reference files not being put into the output (they now output, they used to incorrectly not)
Fix lint mode - now reports all errors
Fixed a small scope issue with & {} selector rulesets incorrectly making mixins visible - regression from 1.6.2
Browser - added log level "debug" at 3 to get less logging, The default has changed so unless you set the value to the default you won't see a difference
Browser - logLevel takes effect regardless of the environment (production/dev)
Browser - added postProcessor option, a function called to post-process the css before adding to the page
Browser - use the right request for file access in IE

Fix issue with calling toCSS twice not working in some situations (like with bootstrap 2)

The Rhino release is fixed!
ability to use uppercase colours
Fix a nasty bug causing syntax errors when selector interpolation is preceded by a long comment (and some other cases)
Fix a major bug with the variable scope in guards on selectors (e.g. not mixins)
Fold in & when () { to the current selector rather than duplicating it
fix another issue with array prototypes
add a url-args option which adds a value to all urls (for cache busting)
Round numbers to 8 decimal places - thereby stopping javascript precision errors
some improvements to the default() function in more complex scenarios
improved missing '{' and '(' detection

support ^ and ^^ shadow dom selectors
fix sourcemap selector (used to report end of the element or selector) and directive position (previously not supported)
fix parsing empty less files
error on (currently) ambiguous guards on multiple css selectors
older environments - protect against typeof regex returning function
Do not use default keyword
use innerHTML in tests, not innerText
protect for-in in case Array and Object prototypes have custom fields

Properties can be interpolated, e.g. @{prefix}-property: value;
a default function has been added only valid in mixin definitions to determine if no other mixins have been matched
Added a plugins option that allows specifying an array of visitors run on the less AST
Performance improvements that may result in approx 20-40% speed up
Javascript evaluations returning numbers can now be used in calculations/functions
fixed issue when adding colours, taking the alpha over 1 and breaking when used in colour functions
when adding together 2 colours with non zero alpha, the alpha will now be combined rather than added
the advanced colour functions no longer ignore transparency, they blend that too
Added --clean-option and cleancssOptions to allow passing in clean css options
rgba declarations are now always clamped e.g. rgba(-1,258,258, -1) becomes rgba(0, 255, 255, 0)
Fix possible issue with import reference not bringing in styles (may not be a bugfix, just a code tidy)
Fix some issues with urls() being prefixed twice and unquoted urls in mixins being processed each time they are called
Fixed error messages for undefined variables in javascript evaluation
Fixed line/column numbers from math errors

Added source-map-URL option
Fixed a bug which meant the minimised 1.5.0 browser version was not wrapped, meaning it interfered with require js
Fixed a bug where the browser version assume port was specified
Added the ability to specify variables on the command line
Upgraded clean-css and fixed it from trying to import
correct a bug meaning imports weren't synchronous (syncImport option available for full synchronous behaviour)
better mixin matching behaviour with calling multiple classes e.g. .a.b.c;

sourcemap support
support for import inline option to include css that you do NOT want less to parse e.g. @import (inline) "file.css";
better support for modifyVars (refresh styles with new variables, using a file cache), is now more resiliant
support for import reference option to reference external css, but not output it. Any mixin calls or extend's will be output.
support for guards on selectors (currently only if you have a single selector)
allow property merging through the +: syntax
Added min/max functions
Added length function and improved extract to work with comma seperated values
when using import multiple, sub imports are imported multiple times into final output
fix bad spaces between namespace operators
do not compress comment if it begins with an exclamation mark
Fix the saturate function to pass through when using the CSS syntax
Added svg-gradient function
Added no-js option to lessc (in browser, use javascriptEnabled: false) which disallows JavaScript in less files
switched from the little supported and buggy cssmin (previously ycssmin) to clean-css
support transparent as a color, but not convert between rgba(0, 0, 0, 0) and transparent
remove sys.puts calls to stop deprecation warnings in future node.js releases
Browser: added logLevel option to control logging (2 = everything, 1 = errors only, 0 = no logging)
Browser: added errorReporting option which can be "html" (default) or "console" or a function
Now uses grunt for building and testing
A few bug fixes for media queries, extends, scoping, compression and import once.

Notes relative to last stable release (1.3.3)

• support for :extend() in selectors (e.g. input:extend(.button) {}) and &:extend(); in ruleset (e.g. input { &:extend(.button all); })
• Process ./ when having relative paths
• add isunit function for mixin guards and non basic units
• extends recognise attributes
• exception errors extend the JavaScript Error
• remove es-5-shim as standard from the browser
• Fix path issues with windows/linux local paths
• strictMaths option added - maths is now only done inside brackets. This means font: statements, media queries and the calc function can use a simpler format without being escaped. Enable this with --strict-math=on in lessc and strictMath:true in JavaScript.
• units are calculated, e.g. 200cm+1m = 3m, 3px/1px = 3. strictUnits option added - If you use units inconsistently you will get an error. to detect these errors use --strict-units=on in lessc or strictUnits:true in JavaScript
• (~"@var") selector interpolation is removed. Use @{var} in selectors to have variable selectors
• default behaviour of import is to import each file once. @import-once has been removed.
• You can specify options on imports to force it to behave as css or less @import (less) "file.css" will process the file as less
• variables in mixins no longer 'leak' into their calling scope
• added data-uri function which will inline an image into the output css. If ieCompat option is true and file is too large, it will fallback to a url()
• significant bug fixes to our debug options
• other parameters can be used as defaults in mixins e.g. .a(@a, @b:@a)
• an error is shown if properties are used outside of a ruleset
• added extract function which picks a value out of a list, e.g. extract(12 13 14, 3) => 3
• added luma, hsvhue, hsvsaturation, hsvvalue functions
• added pow, pi, mod, tan, sin, cos, atan, asin, acos and sqrt math functions
• added convert function, e.g. convert(1rad, deg) => value in degrees
• lessc makes output directories if they don't exist
• lessc @import supports https and 301's
• lessc "-depends" option for lessc writes out the list of import files used in makefile format
• lessc "-lint" option just reports errors
• support for namespaces in attributes and selector interpolation in attributes
• other bug fixes

• fix syncImports and yui-compress option, as they were being ignored
• fixed several global variable leaks
• handle getting null or undefined passed as the options object

• if you don't pass a strict maths option, font size/line height options are output correctly again
• npmignore now include .gitattributes
• property names may include capital letters
• various windows path fixes (capital letters, multiple // in a path)