clause of their publishing contract for Steam, and took steps to restrict sale of the game in over 20 regions. Games that feature mature themes with primary characters that visually appear to be underaged, even if the game's narrative establishes them as adults, have been banned by Valve. In March 2019, Valve faced pressure over Rape Day, a planned game described as being a dark comedy and power fantasy where the player would control a serial rapist in the midst of a zombie apocalypse. Journalists questioned how the hands-off approach would handle this case; Valve ultimately decided against offering the game on Steam, arguing that while it "[respects] developers' desire to express themselves", there were "costs and risks" associated with the game's content, and the developers had "chosen content matter and a way of representing it that makes it very difficult for us to help them [find an audience]". Platforms and devices Microsoft Windows client Steam originally released exclusively for Microsoft Windows in 2003, but has since been ported to other platforms. More recent Steam client versions use the Chromium Embedded Framework. To take advantage of some of its features for newer interface elements, Steam uses 64-bit versions of Chromium, which makes it unsupported on older operating systems such as Windows XP and Windows Vista. Steam on Windows also relies on some security features built into later versions of Windows. Steam support for XP and Vista were dropped in 2019. While users still on those operating systems are able to use the client, they do not have access to newer features. Around only 0.2% of Steam users were affected by this when it began. macOS client On March 8, 2010, Valve announced a client for Mac OS X. The announcement was preceded by a change in the Steam beta client to support the cross-platform WebKit web browser rendering engine instead of the Trident engine of Internet Explorer. Before this announcement, Valve teased the release by e-mailing several images to Mac community and gaming websites; the images featured characters from Valve games with Apple logos and parodies of vintage Macintosh advertisements. Valve developed a full video homage to Apple's 1984 Macintosh commercial to announce the availability of Half-Life 2 and its episodes on the service; some concept images for the video had previously been used to tease the Mac Steam client. Steam for Mac OS X was originally planned for release