2.1.687 Part 1 Section 18.8.7, cellStyle (Cell Style)
a. The standard does not limit the length of the value for the @name.
Office limits the value of @name to 255 characters.
b. The standard states that the builtinId attribute is any 32-bit unsigned integer.
Office limits the values of the builtinId attribute to greater than or equal to zero and less than or equal to 53.
c. The standard states that the iLevel attribute indicates that formatting is for an outline style, regardless of the value of the builtIn attribute.
Office will ignore the iLevel attribute if the style is not either the RowLevel or ColLevel built-in styles (builtIn=1 or =2).
d. The standard states that the values of the iLevel attribute are defined by the XML Schema unsigned int datatype.
Office limits the iLevel attribute to the values 0 through 7.
e. The standard does not define built-in styles 12, 13, and 14.
Office defines built-in styles 12 = "Emphasis 1", 13 = "Emphasis 2", 14 = "Emphasis 3".
f. The standard does not place uniqueness restrictions on the xfId attribute.
Office requires that the xfId attribute must be unique with respect to the xfId values in all other cellStyle elements.