atw: cell margins /cell spacing

I am cleaning up some tables with lots of text.
Is there a guideline for the margin in each cell.  Here I mean the margin to
be the space between the text and the cell, also termed cell padding.

Is it at least half a character high, or a percentage, or what?

The only reference I could find in the Style Manual refers to 'appropriate
cell spacing ...' for online tables.  Cell spacing is not quite the same as
cell padding/cell margin.

Are the guidelines for tales printed without borders any different?

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