<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--add>
      ^{add}
