PAL VHS machines support this (or any) format for closed caption recording. Like all teletext fields, teletext captions can't be stored by a standard 625 line VHS recorder (due to the lack of field shifting support); they are available on all professional S-VHS recordings due to all fields being recorded. Recorded Teletext caption fields also suffer from a higher number of caption errors due to increased number of bits and a low SNR, especially on low-bandwidth VHS. This is why Teletext captions used to be stored separately on floppy disk to the analogue master tape. DVDs have their own system for subtitles and captions, which are digitally inserted in the data stream and decoded on playback into video. For older televisions, a set-top box or other decoder is usually required. In the US, since the passage of the Television Decoder Circuitry Act, manufacturers of most television receivers sold have been required to include closed captioning display capability. High-definition TV sets, receivers, and tuner cards are also covered, though the technical specifications are different (high-definition display screens, as opposed to high-definition TVs, may lack captioning). Canada has no similar law but receives the same sets as the US in most cases. During transmission, single byte errors can be replaced by a white space which can appear at the beginning of the program. More byte errors during EIA-608 transmission can affect the screen momentarily, by defaulting to a real-time mode such as the "roll up" style, type random letters on screen, and then revert to normal. Uncorrectable byte errors within the teletext page header will cause whole captions to be dropped. EIA-608, due to using only two characters per video frame, sends these captions ahead of time storing them in a second buffer awaiting a command to display them; Teletext sends these in real-time. The use of capitalization varies among caption providers. Most caption providers capitalize all words while others such as WGBH and non-US providers prefer to use mixed-case letters. There are two main styles of line 21 closed captioning: Roll-up or scroll-up or paint-on or scrolling: Real-time words sent in paint-on or scrolling mode appear from left to right, up to one line at a time; when a line is filled in roll-up mode, the whole line scrolls up to make way for a new line, and the line on top is erased. The lines usually appear at the bottom