
Compute weekdays correctly for calendars where some days (intercalary/epagomenal) are excluded from the weekday cycle. Use when implementing or debugging weekday logic with “skipped days”, “epagomenal”, “intercalary”, or “non-weekday” days.
Designs and implements complete calendar and timekeeping calculation modules for the Library of Time project, including algorithms, date conversions, and tests. Use when working on calendar logic, adding a new calendar, or one-shotting an entire calendar implementation from a prompt. Treat `CalendarAPI/Calendars/*`, `CalendarAPI/Timekeeping/*`, and `CalendarAPI/Other/*` as a single Calendar API layer.
Use user-provided month names or labels in calendar implementations and output. Use when implementing or updating a calendar and the user has given a list of month names (including for leap months), so the implementation does not default to numeric-only output.
Encodes conventions and logic patterns for building calendars and timekeeping systems in the Library of Time project, including preferred use of utilities like createAdjustedDateTime, timezone handling, and epoch selection. Use when implementing or refactoring calendar logic so behavior matches existing systems.
Step-by-step workflow for adding a new calendar or timekeeping system to the Library of Time, including creating the Docs entry, regenerating nodeData, wiring the main function into the CalendarAPI layer and nodeUpdate.js, and adding tests. Use when introducing a new calendar node to the site.
Rules and pitfalls for implementing lunisolar (or similar) calendars that are defined by explicit anchor dates and a fixed cycle (e.g. Metonic), not by astronomical events like equinox or "first new moon after X". Use when implementing or fixing such calendars (e.g. Babylonian, or any spec that gives "date X = year Y month 1 day 1").
Catalogs common implementation patterns used by existing calendars and timekeeping systems in the Library of Time, with examples and guidance on when to use each pattern. Use when choosing how to structure a new calendar’s algorithm.