Development Group. The PNG group officially rejected APNG as an official extension on April 20, 2007. There have been several subsequent proposals for a simple animated graphics format based on PNG using several different approaches. Mozilla Firefox added support for APNG in version 3 trunk builds on March 23, 2007. However, because libpng is the PNG Group's reference implementation of the official specification, APNG support can never be supported in the main libpng distribution so long as it remains unratified by the Group. Iceweasel 3 supports APNG by using Mozilla's unofficial variant of libpng. In 2008 WorldDMB adopted APNG as a backward compatible extension to enable animation as part of the MOT SlideShow user application for Digital Radio. "APNG 1.0 Specification - Animated Portable Network Graphics" is included as normative Annex A in the ETSI standard TS 101 499 V2.2.1. In 2010 Commercial Radio Broadcasters in Sydney began to include APNG animations in DAB+ digital radio broadcasts. These APNG animations are carried by the "MOT slideshow" application which accompanies the audio services. It is expected that other cities in Australia will follow in early 2011. Mozilla's role in extending the PNG format to APNG echoes Netscape's much earlier role in popularizing animated GIFs. In 2016, Apple adopted the APNG format as the preferred format for animated stickers in iOS 10 iMessage apps. On March 15, 2017, APNG support was added to Chromium. File format The APNG specification follows the PNG File format introducing three new ancillary chunks: The animation control chunk (acTL) precedes the IDAT(s) of the default image and is a kind of "marker" that this is an animated PNG file. It also contains the number of frames and the number of times to loop the animation (0 meaning infinite). The frame control chunk (fcTL) precedes each frame and contains its metadata : dimensions ; position (relative to the default image); duration; if once over it is cleared to black, replaced by the previous frame or drawn over by the next frame ; and if its transparency applies. The frame data chunk (fdAT) storing frame's content. It starts with a sequence number, then has the same structure as the default image's IDAT chunk(s). Sequence numbers apply to both frame control and frame data chunks, which together follow a common sequence, thus enabling the order and timing of frames to be recovered should an APNG-unaware PNG editor re-order them as