For information about AppleCare+ for a MacBook Air, see: AppleCare Products - Mac - Apple including the following:
Every Mac comes with one year of hardware repair coverage through its limited warrantyand up to 90 days of complimentary technical support. AppleCare+ for Mac extends your coverage from your AppleCare+ purchase date and includes unlimited incidents of accidental damage protection, each subject to a service fee of $99 for screen damage or external enclosure damage, or $299 for other accidental damage, plus applicable tax.1 In addition, you’ll get 24/7 priority access to Apple experts by chat or phone.2
For full legal details, see: https://www.apple.com/legal/sales-support/applecare/applecareplus/2209/220907_applecareplusmac_us.pdf including the following mention of liquid damage and cosmetic damage:
If during the Plan Term you submit a valid claim notifying Apple that the Covered Device has failed due to accidental damage from handling resulting from an unexpected and unintentional external event (e.g., drops and damages caused by liquid contact from spills) (“ADH”), Apple will, at its discretion and subject to the service fee described below, either (i) repair the defect using new or previously used genuine Apple parts that have been tested and pass Apple functional requirements, or (ii) exchange the Covered Device with a replacement product that is new or comprised of new and/or previously used genuine Apple parts and has been tested and passed Apple functional requirements. Exclusions apply as described below.
Two of the exclusions are:
Apple will not provide Hardware Service or ADH Service in the following circumstances:
(a) To protect against normal wear and tear, or to repair cosmetic damage not affecting the functionality of the Covered Equipment;
...
(d) To repair damage, including excessive physical damage (e.g., products that have been crushed, bent or submerged in liquid), caused by reckless, abusive, willful or intentional conduct, or any use of the Covered Equipment in a manner not normal or intended by Apple;
Read the originals of the above two documents for full details.