Data binding checkboxes in svelte

in a svelte/sapper form I want to send data to a user model

<input type="text" bind:value={user.label}>

..works as expected. But how to send user.offer_ids

let offer_ids = [];

{#each offers as offer}
  <label>
   <input type=checkbox bind:group={offer_ids} value="{offer.id}">{offer.label}
  </label>
{/each}

I can't find any svelte sample how to do this job, which I think is basic in forms.. Thanks for help