最近了解到原來OPT離開美國的時間都算是90天的unemployment period，特意去查了查官方文件，看到OPT Policy Guidance的7.1.8說明如下：
7.1.8. How does travel outside the United States impact the period of
Time spent outside the United States during an approved period of postcompletion OPT counts as unemployment against the 90/120-day limits,
unless the student is either:
Employed during a period of leave authorized by an employer; or
Traveling as part of his or her employment.
第二點很容易理解，公司出差要出境的話不算；但第一點說的是PTO期間離境，就不算90天嗎？如果是週末開車去加拿大，這樣不需要「authorized by an employer」，也不算PTO的話，就算入90天了？