ks-placeholder()
    if selector() == "&"
        error( "placeholder() must be called from a ruleset!" )
    &::-webkit-input-placeholder
        {block}
    &:-moz-placeholder
        {block}
    &::-moz-placeholder
        {block}
    &:-ms-input-placeholder
        {block}

placeholder = ks-placeholder unless ks-no-conflict