Column spanning in summary row

Use case

If you have very narrow columns (e.g. the SelectColumn which has a width of 35px) you need to put the content of your summary row in the second/third/etc. column (see screenshot below), because it won't fit in those narrow columns. It would be nice if we can span that text across columns in the summary row as we can do in the table itself like you've done in the column spanning demo. That way the summary row text can always start from the far left regardless of the size of the columns.

Proposed solution

Have the option to specify that the content of a column in the summary row should span across multiple columns. So that it can look something like this: