cellspacing Cell Spacing (NISO JATS table model)
Width of space between cells in a table. (This attribute is based on and intended to be converted easily to the XHMTL cellspacing attribute.)
Although the Tag Set can enforce only that this attribute contain any text, numbers, or special characters, best practice is to constrain this value to a counting number (positive integer).
OPTIONAL on element: <table>
|Thickness, measured in pixels, of the space between cells in a table.
|@cellspacing is an optional attribute; there is no default.