v1.7.5

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

v1.7.4

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

v1.7.3

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

v1.7.2

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)

v1.7.1

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

v1.7.0

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

v1.6.3

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

v1.6.2

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

v1.6.1

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

v1.6.0

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