Format.RuleA rule consists of a styled prefix, a styled suffix, and a style. Rules are applied to strings using functions defined in Output_ops.
module Affix : sig ... endAn affix is either a prefix or a suffix.
val sexp_of_t : t -> Sexplib0.Sexp.tRule creation: Most rules have a style, and maybe a prefix. For instance, a line_next rule might have a bold "+" prefix and a green style.
val blank : tval unstyled_prefix : string -> t