Hi, Sim.
Thanks for your reply! :^D
First of all, sorry for my poor understanding... :(
I have an additional question. Is that okay?
I followed your advice and made it like this. (left out stuff not necessary for this question...)
columns: [
{ type: 'checkbox' }, { field: 'Id', isPrimaryKey:true }, { field: 'Name' }, ... ], |
This produced a nice table, but I have a problem here...
I want the number of checkboxes to count automatically... like this.
(I didn't think I could explain it well, so I drew a picture.)

What should I do next in this situation?
some additional explanation is needed... &-|