In this screenshot the line 684 (covered by the popup) is "&:extend(.clearfix all);"
Also, if you import a A.less into B.less, if for example .foo is the first class of A.less containing an &:extend() (and .foo being marked as invalid), then all the elements which are placed after .foo aren't imported into B.less: hence in B.less you see them as errors.
For example in bootstrap, in mixins.less the first error is at
Eclipse Juno - LESS plugin v. 1.0.19
Mixins using extend are marked as invalid.
In this screenshot the line 684 (covered by the popup) is "&:extend(.clearfix all);"
Also, if you import a A.less into B.less, if for example .foo is the first class of A.less containing an &:extend() (and .foo being marked as invalid), then all the elements which are placed after .foo aren't imported into B.less: hence in B.less you see them as errors.
For example in bootstrap, in mixins.less the first error is at
==> Then, if we import bootstrap/mixins.less somewhere, .make-row won't be seen as a valid mixin, because it is placed after a validation error.