How to set a multicol cell to span all columns

[ysalmon]

I have various tables to typeset where the first row should be a multicell spanning all the columns. The numbers of columns varies from table to table.

I would like to say something like

\SetTblrInner[mytable]{cell{1}{1} = {c=*, r=1}{c}}

but this does not work.

[ysalmon]

Found it : the counters mentioned in section 3.8 seem available at spec time too. So I can say

\SetTblrInner[mytable]{cell{1}{1} = {c=\value{colcount}, r=1}{c}}