Opps, I haven't written a test case.
But it's already too late here.
I'm not sure if this fits your plan, but the result met my expectation.

@Flithor Cool, I'm just a lurker these days but this looks useful to me. It deserves some tests, in particular when dealing with more irregular merged ranges. Suggest to add some tests later when you can, I guess there is no rush

@andersnm added the test cases and fix bug, I think it worth to merge and publish.

Our project management strategy prefers to use NuGet packages directly.

@andersnm I wanted to ask if you could review and merge this pending pull request.
And would it be possible to publish a new release to NuGet? So that the community can benefit from the update.
Thank you.

@Flithor Apologies, I'm personally unable to review and merge these days, but I'm sure @appel1 will take a look at this at some point.

Haven't had time. Sorry.

I think it's a good addition but want to look at the code before I merge.

My initial design include three fill mode: horizontal fill, vertical fill, and full fill.

However, I've found that scenarios on read the sheet as a DataTable almost always for reading formatted table data, and the first two fill mode seemed no uses. So, only retain the full fill.

I'm not sure if horizontal and vertical fill have any other uses.

@appel1 Hello? Any progress?

There were long times ago......