A part of Extend document is error at the "Selector Interpolation with Extend".

[mingtianyihou33]

Selector Interpolation with Extend

@variable: .bucket;
@{variable} { // interpolated selector
  color: blue;
}
.some-class:extend(.bucket) {}

will output

.bucket,
.some-class {
  color: blue;
}

It's matched!!!
My version of less is 3.12.2.