mixin icon(id)
    -
        let href    = 'icons.svg#' + id
        let classes = {
            'o-icon':    true,
            'u-d-block': attributes.block,
        }
        if (attributes.class) {
            classes[attributes.class] = true;
        }

    svg(class=classes width="1.142857143em" height="1.142857143em" aria-hidden="true")
        use(href=href)