Patdiff_kernel.FormatSourcePatdiff_format is the home of all the internal representations of the formatting that will be applied to the diff. ie. prefixes, suffixes, & valid styles.
A rule consists of a styled prefix, a styled suffix, and a style. Rules are applied to strings using functions defined in Output_ops.
Rules are configured in the configuration file. Default values are provided in Configuration.
A column rendered to the left of the line-number / +/- gutter.