"An extra layer pair named FILMMASK_TOP and FILMMASK_BOTTOM is available for use in whatever means you wish. These two layers are optional and do not have to be used or defined. You can also define up to a maximum of sixteen user-defined mask layers, which you add according to your design flow requirements. This may include, but not be limited to, applications associated with via plugging, hard gold, soft gold, silver, or other soldermask alternatives. "
