In The Mef, When Does One Celebrate A Low, High, And Solemn High Mass?

[Gabriela]

Are there days when it's forbidden to perform a Low MEF? Are there days when one MUST perform a Solemn High MEF? I'm trying to figure out what to expect when I go to the MEFs celebrated by the Canons Regular of the New Jerusalem.

[cappie]

High Mass is usually celebrated at the main Mass on Sundays and major feasts