Gregorian calendar

Construction

Use CivilDateTime::fromGregorian() and gregorian(); parse with Eram\Daynum\Calendar\Gregorian\GregorianView. The calendar identifier and locale family are both gregorian. Default string format is Y-m-d.

Proleptic semantics

Daynum applies the Gregorian leap rule to all supported years, including dates before its historical adoption. It does not model a Julian/Gregorian cutover or regional skipped dates. Astronomical year numbering includes year 0 (1 BCE); year -1 represents 2 BCE.

Leap year rule

A year divisible by 4 is leap unless divisible by 100 but not 400.

<?php
require 'vendor/autoload.php';

use Eram\Daynum\CivilDateTime;

var_export(CivilDateTime::isValidGregorian(1900, 2, 29));
echo "\n";
var_export(CivilDateTime::isValidGregorian(2000, 2, 29));
echo "\n";
echo CivilDateTime::fromGregorian(0, 1, 1)->gregorian()->format('Y-m-d'), "\n";

false
true
0000-01-01

Range

GregorianCalendar::MIN_YEAR is -9999 and MAX_YEAR is 9999, inclusive for construction. supportedRange() returns the corresponding inclusive JDN bounds. Low-level reverse conversion and JDN arithmetic can produce values outside those construction limits; check isInSupportedRange() rather than relying on every accessor to throw. Integer/timestamp limits of the PHP platform still apply.

Read formatting, arithmetic and algorithms.