[Jeffhs]

If you were viewing broadcast TV and saw these lines, dots, etc. at the top of the picture they would be what are known as Vertical Interval Test Signals (VITS). These show in the vertical blanking interval and are (or were) used to adjust such things as video levels and so forth. These signals, when seen in the blanking interval of non-broadcast images such as those from DVDs, however, are, as has been noted, for text, closed captioning, and other advanced functions of today's TVs. Some GE televisions of the '70s had a feature known as "VIR", which was supposed to automatically control hue, brightness, saturation, etc. of a color picture according to a signal sent by the broadcaster in the vertical blanking interval. I do not know if the VIR signal was ever visible in the blanking bar, in addition to network VITS or otherwise.

VITS are still used in broadcast TV today, but are normally invisible to viewers since the blanking bar is ordinarily off the top of the screen on properly scanned TVs, as were the older versions of these signals. The signals are likely used for closed captioning, text, etc. as they are for DVDs and other non-broadcast applications.

The "white glare" at the bottom of your TV picture when you are trying to adjust vertical height and linearity is called foldover. It occurs when these controls are incorrectly set (normally far too high) such that the lower part of the image on the television screen is actually, literally, folded over onto itself. The cure is to adjust the height/linearity controls so the picture just overscans the CRT mask at top and bottom. Since these controls normally interact with each other, you may need to fiddle with the adjustments (trial and error) until you get the desired result.