T5: How to set generated component id

[Peter Kanze]

Hello,

I want to add some blocks with a generated id. like this:

<t:loop source="thumbnailPictures" value="thumbnail" index="thumbIndex">
      <t:block id="image${thumbIndex}">
          <img t:type="filesystemImage"product="product"
position="thumbIndex" type="bigPictureType" />
      </t:block>
</t:loop>

But I get the following error message:
Block id 'image${thumbIndex}' is not valid; block ids must be valid Java
identifiers: start with a letter, and consist of letters, numbers and
underscores.

How can I give my block an id based on the current thumbIndex?

Any examples?

Thanks!
Peter