Perfect Continuous Tense.
The Perfect Continuous Tense mainly denotes that something has (had/will have) done continually (often/frequently, etc.) for/since/in some (certain or uncertain) period of time.
It is very common to use a preposition (for, since, etc.) or an adverb (lately, recently, etc.) with, at the begging of or at the end of a sentence.
As there are three Tenses, so are there three patterns, as:
1. Present Perfect Continuous Tense.
2. Past Perfect Continuous Tense.
3. Future Perfect Continuous Tense.
We can learn each of them in next three lessons in detail with examples.