When creating a new product template without specifying the 'Variant reference mask', a default value for 'Variant reference mask' will be automatically generated according to the attribute line settings on the product template. The mask will then be used as an instruction to generate default code of each product variant of the product template with the corresponding Attribute Code (of the attribute value) inserted. Besides the default value, 'Variant reference mask' can be configure to your liking, make sure puting Attribut Name inside '[]' mark.

Example:

Creating a product named 'A' with two attributes, 'Size' and 'Color':

Product: A
Color: Red(r), Yellow(y), Black(b) #Red, Yellow, Black are the attribute
       value, 'r', 'y', 'b' are the corresponding code
Size: L (l), XL(x)

The automatically generated default value for the Variant reference mask will be [Color]-[Size] and then the 'default code' on the variants will be something like r-l b-l r-x ...

If you like, you can change the mask value whatever you like. You can even have the attribute name appear more than once in the mask such as , fancyA/[Size]~[Color]~[Size], when saved the default code on variants will be something like fancyA/l~r~l (for variant with Color "Red" and Size "L") fancyA/x~y~x (for variant with Color "Yellow" and Size "XL").

when the code attribute is changed, it automatically regenerates the 'default code'.