When does 시 become 세?

Question

In my Talk To Me In Korean book 'Real Life Conversations For Beginners', there is a dialog which includes the translation: "Are you a student?" / 학생 이세요

I was expecting the sentence to be 학생 이시에요, if the honorific suffix (으)시 is to be used. Why did 시에 become 세? I suspect this is a contraction, yes? Are there general rules for these type of contractions for pre-final endings?

Answer 1

1) 우리 아빠는 학생이시다 My father is a student

2) 이시다 + 어요 (politeness suffix) -> 이시어요 -> 이셔요 -> 이세요

https://www.italki.com/question/438903