less.js/test/less/merge.less

.first-transform() {
  transform: rotate(90deg) skew(30deg) !merge(space);
}
.second-transform() {
  transform: scale(2,4) !merge(space);
}
.third-transform() {
  transform: scaleX(45deg);
}
.fourth-transform() {
  transform: scaleX(45deg) !merge(comma);
}
.fifth-transform() {
  transform: scale(2,4) !important !merge(space);
}
.first-background() {
  background: url(img1.png) !merge(comma);
}
.second-background() {
  background: url(img2.png) !merge(comma);
}

.test1 {
  // Can merge values with space separator 
  .first-transform();
  .second-transform();
}
.test2 {
  // Wont merge values without !merge directive, for backwards compatibility with css
  .first-transform();
  .third-transform();
}
.test3 {
  // Can merge values with comma separator
  .first-background();
  .second-background();
}
.test4 {
  // Wont merge values from two sources with different seperators
  .first-transform();
  .fourth-transform();
}
.test5 {
  // Wont merge values from two sources with the same seperators but different properties
  .fourth-transform();
  .first-background();
}
.test6 {
  // Wont merge values from sources that merked as !important, for backwards compatibility with css 
  .first-transform();
  .fifth-transform();
}
.test7 {
  // Wont merge values from mixins that merked as !important, for backwards compatibility with css 
  .first-transform();
  .second-transform() !important;
}
.test8 {
  // Ignores !merge if no peers found
  .second-transform();
}