Why in Bootstrap does not exist classes like

.row-xs-start {
    justify-content: flex-start;
}

.row-xs-center {
    justify-content: center;
}

.row-xs-end {
    justify-content: flex-end;
}

And you could rename classes .row-xs-top, .row-xs-center, .row-xs-bottom to .row-xs-top, .row-xs-middle, .row-xs-bottom && .col-xs-top, .col-xs-center, .col-xs-bottom to .col-xs-top, .col-xs-middle, .col-xs-bottom