This is just an FYI, not a criticism....
Many commercial "balsamic" vinegars aren't real balsamic vinegar because they are made from regular wine vinegar with grape must added (and sometimes coloring and sugar). Most common "balsamics" of this type are made with red wine, must and carmel coloring. "White balsamics" are made with white wine.
Real balsamic vinegar is not made with red or white wine vinegar. It's made from the must of white trebbiano grapes, cooked down and aged in wooden barrels.
In fact, some of the so-called balsamics in the supermarket contain no must at all, but are red wine vinegars with coloring and sugar added. Always look for must in the ingredient list. If it's not there, don't buy it.
Real aged balsamic vinegar is usually quite expensive and is often used as a condiment and not in salad dressing, marinades, etc.
The supermarket balsamics (wine and must) have beaten out real balsamics in taste tests, however, so no one should hesitate to use them. Just make sure you read the label and buy one that contains grape must.