What is an evaporation line on a pregnancy test?

"Evaporation lines are common and can occur with any pregnancy test. An evaporation line is a line that appears in the results window of a pregnancy test as the urine dries. It can leave a faint, colorless line."

The point is this- posting a test and asking if it is a positive or an evap doesn't make much sense. If evaps happen as the urine is DRYING, there isn't a point in asking if a test is an evap. If there is a possibility of an evap, that means the test is more than likely past the recommended time for reading the results. Truth is, no one is going to know for sure if a test is an evap if they don't know how old the test is, unless the time frame is specified. If people stop taking pictures of tests after the recommended time frame and posting them, there wouldn't be so much confusion over whether or not a test is a positive or an evap. Does anyone else see my point? I am only saying because I see so many people asking if their test is an evap or not.