Okay, test your skills. Yes or no? The following is an example of useful and correctly written documentation: "Tom S. arrived twenty minutes late to work today and was witnessed, by several employees, damaging another vehicle while trying to park his car. He was heard yelling obscenities from within car. When I met with him immediately after the incident, I could smell alcohol on his breath." .... Yes. This is an example of documentation that is specific and clear. There are no subjective or opinionated comments or conclusions about the employee's condition. It is written in a factual, unemotional way, with attention to that which can be sensed--in this case what can be seen, heard, and smelled.
Okay, try this one: "Tom Smith arrived at work late with reports by others of being drunk. He scraped a car in the parking lot and when confronted by me, after the incident, became defensive and acted immature showing that he had something to hide and to get others to "back off". He denied he was drunk, but admitted he had been drinking before midnight, which is when he stated his last drink occurred."
This documentation lacks specific details and instead appears to be conjecture; it would be difficult to defend. It would not support a disciplinary action or a reasonable-suspicion drug test.
To really get a grip on performance documentation, have your supervisors able to quickly access instructions on this document by using your companies internal web site or a special section for supervisors where supervisory skills can be found and learned quickly. This is very easy to do with a product such as the 14 Vital Skll for Supervisors Training Online Flash course. The author lets you view it completely free.