Table cell extensions

[KentSpiel]

Table cells are classified as character styles. They are marked by tags that begin \tc .
Since tables cell extensions they cannot begin with z, I propose allowing table cell extensions that begin: \tcz . Also, since table cells are always numbered by column, I propose that such extensions must be terminated by an index number for the column.

I also propose that a table header cell extensions be allowed, which must begin \thz , and which likewise must terminate in a column index number.

My use case is for data tables in peripheral book. I would like to classify some cells as non-vernacular in order to exclude their contents from the Paratext project wordlist.