@_ parametric condition not functional

[succinct]

According to the LESS documentation, the following is allowable:

.mixin (dark, @color) {
color: darken(@color, 10%);
}
.mixin (light, @color) {
color: lighten(@color, 10%);
}
.mixin (@_, @color) {
display: block;
}

This allows you to have a parametric condition that is applied regardless of what parameter is supplied. However, I'm unable to even TYPE @_ within Netbeans with the plugin loaded; it starts shifting the code color formatting around. Loading a file that has been edited externally breaks when it hits the line with the @_.