Discuss when the requirements of the revenue recognition principle are usually met. Give an example.

Please answer following and make sure to include reference

Under the accrual basis accounting, revenues and expenses are recognized by the following principles:

Revenue recognition: Revenue is recognized when both of the following conditions are met: Revenue is earned and Revenue is realized or realizable.
Expense recognition: Expense is recognized in the period in which related revenue is recognized (this is also known as the Matching Principle).

Respond to the following:

Discuss when the requirements of the revenue recognition principle are usually met. Give an example.
Discuss when the requirements of the expense recognition principle are usually met. Give an example.