<ul .massinput__row .#{"massinput--dim" <> toPathPiece dimIx}>
  $forall (cellCoord, cell) <- cells
    <li .massinput__cell data-massinput-coord=#{toPathPiece cellCoord}>
      ^{cell}
  $maybe add <- addWidget
    <li .massinput__cell.massinput__cell--add>
      ^{add}
