Why the year 2100 doesn't have a 53 week ?

Hello,

according to the function date_get_week,

a year has a week 53 only if the 31 december of this year is a thursday.

the exception is : if the 31 december is a friday AND the year is a bisextile year.

However, the friday 31.12.2100 is a friday of a bisextile year, and has only 52 weeks according to the function.

Could you explain me the point I missed in the rule ?

Thank you

Amaury