2.1.158 Part 4 Section 2.4.50, tblLayout (Table Layout Exception)
a. The standard states that the table layout exception can be used to set any table row's table layout to autofit or fixed.
Word ignores this element if it is not in the first row of the table or if its value is autofit. If the value is not ignored, then it applies to the whole table.
b. The standard states that if the tblLayout element is omitted, then the value defaults to autofit.
In Word, if the tblLayout element is omitted, then the layout algorithm is determined by the default set of table properties on the parent table.