Function resolve_reserved 

fn resolve_reserved(code: &str) -> Option<Arc<dyn Calendar>>

The two rule-based calendars, reachable by a reserved code so that the whole substrate is namable in one expression language.

EVERYDAY is the calendar on which every day is a business day; WEEKDAYS the one on which only weekends are not. Both are longer than four characters and carry no dot, so neither can collide with the four-character FpML code space or a qualified BASE.SUFFIX market code. They join and link like any other token — "GBLO,WEEKDAYS" is London closed on its own holidays and every weekend.