Something about AVR (I found it somewhere on internet)Automatic Visa Revalidation
US Department of State regulations permit certain non-immigrants to re-enter the United States after a 30-day or less visit to Canada, Mexico, or other adjacent islands (other than Cuba) without having to obtain a new visa prior to re-entry. This is called automatic visa revalidation (AVR).
Automatic revalidation applies in two ways.
1. If you have a visa sticker in your passport that matches your current status, but has expired, that visa sticker is considered to be automatically revalidated to a current date for your return to the U.S.
2. If you have changed status while in the U.S., and you have a visa sticker that matches your old status (either expired or unexpired), that visa sticker is considered to be automatically changed to a stamp matching the new status and revalidated to a current date for your return to the U.S. even though it is not the same as your current status and has, perhaps, expired.
Individuals seeking to benefit from this provision must retain their I-94 when leaving the U.S. as it is essential for re-entry. In addition, all other travel documents relevant to the particular status (passport, DS-2019 for J-1s, I-797 for H-1Bs etc.) must be carried and properly endorsed. When requesting a travel letter from the International Services Office, please state that you will be using the AVR program so your letter may reflect this.
Individuals traveling on passports issued by Iraq, Iran, Syria, Libya, Sudan, North Korea and Cuba may not benefit from this provision. Anyone who is visiting Canada or Mexico in order to apply for a new visa may no longer benefit from automatic revalidation. Please note that persons in H status are only eligible for automatic visa revalidation in Canada and Mexico and not in the adjacent islands. Check the U.S. State Department Website for the most recent information.Telegram
You can print telegram from following link,Its good to have with you in case IO is new and now aware of AVR rule.http://travel.state.gov/visa/laws/telegrams/telegrams_1441.html