Forward compatibility

Telecommunication standards

The introduction of FM stereo transmission, or color television, allowed forward compatibility, since monophonic FM radio receivers and black-and-white TV sets still could receive a signal from a new transmitter.^[2] It also allowed backward compatibility since new receivers could receive monophonic or black-and-white signals generated by old transmitters.^{[citation needed]}

Video gaming

• The Game Boy is able to play certain games released for the Game Boy Color. These games utilize the same cartridge design as games for the original Game Boy, though the plastic used is typically black rather than gray and feature the GBC's logo on the label and packaging; Nintendo officially referred to such titles as being "Dual Mode".^{[5][clarification needed]}
• The Leapster is able to play Leapster L-Max games, and the Leapster L-Max is able to play Leapster2 games.^{[clarification needed]}
• The original PlayStation is compatible with the DualShock 2 controller.^[6] Likewise the PlayStation 3 can be played with a DualShock 4 and DualSense controller.^[7][8][9]
• The Neo Geo Pocket was able to play most games from Neo Geo Pocket Color.^{[citation needed]}
• The WonderSwan is able to play some WonderSwan Color games.^{[clarification needed]}
• The Xbox One can use the controller from the Xbox Series X and Xbox Series S, and likewise an Xbox One controller will work on the Xbox Series X and Series S.^[10]
• The V.Smile Smartridge is compatible with every VTech console and handheld game system. However, it does not support the V.Smile Baby, PC Pal, and V.Flash systems.^[11] Depending on the device inserted, some functions may be limited, reflecting the varied capabilities of each console.^[12]
• The Nintendo Switch can play digital and physical "Nintendo Switch 2 Edition" games. On the Nintendo Switch 2, these versions include both the base game and an upgrade pack, which have better performance, graphics, extra content (the latter of which is usually specific to select first party games), and more. However, the upgrade packs themselves won't run on the original Nintendo Switch, only the base game.^[13]

HTML

HTML is designed to treat all tags in the same way (as inert, unstyled inline elements) unless their appearance or behavior is overridden; either by the browser's default settings, or by scripts or styles included in the page.^[14] This makes most new features degrade gracefully in older browsers. One case where this did not work as intended was script and style blocks, whose contents are meant to be interpreted by the browser instead of being part of the page. Such cases were dealt with by enclosing the contents within comment blocks.^[15] More generally, HTML's forward compatibility follows a "must ignore" design: early HTML specifications required that unrecognized start and end tags be mapped to nothing during tokenization, which is what allowed later elements such as <img> to be introduced without breaking existing browsers.^[3]

As there is no mandatory upgrade of computers or web browsers, many web developers use a graceful degradation or progressive enhancement approach, attempting to make newly created websites that are compatible with older computers and web browsers, usable when JavaScript is disabled or on a slower connection, while still taking advantage of faster hardware and better JavaScript support in more modern web browsers, when available.^[16]

Optical media

Each of the three most common 12 cm optical media formats (CD, DVD, and Blu-ray) was first released in read-only form years before writable forms were available. Within each format, there is both forward and backward compatibility, in that most older read-only drives and players can read (but not write) writable media in the same format, while read/write drives can read (but not write) old read-only media. There is no forward compatibility between formats; a CD player, for instance, can't read a DVD (a newer format), not even the audio tracks. There may be backward compatibility for better marketability (such as a DVD player playing an audio CD), but it is not intrinsic to the standards.^[17]