.opacity(@value) when (isnumber(@value)) and (@value < 1) {
    @percentValue: @value * 100;

    -ms-filter: "progid:DXImageTransform.Microsoft.Alpha(Opacity=@{percentValue})";
    filter: e("alpha(opacity=@{percentValue})");
}

.gradient(@from; @to; @type: 0) when (iscolor(@from)) and (iscolor(@to)) {
    @argbFrom: argb(@from);
    @argbTo: argb(@to);

    filter: e("progid:DXImageTransform.Microsoft.gradient(GradientType=@{type},startColorstr='@{argbFrom}',endColorstr='@{argbTo}')");
}

.alphaImage(@name; @sizingMethod: scale) {
    filter: e("progid:DXImageTransform.Microsoft.AlphaImageLoader(src='@{spritesURL}/img/@{name}.png',sizingMethod='@{sizingMethod}')");
}