Editing GIF (section)

== Metadata ==
[[Metadata]] can be stored in GIF files as a comment block, a plain text block, or an application-specific application extension block.  Several graphics editors use unofficial application extension blocks to include the data used to generate the image, so that it can be recovered for further editing.

All of these methods technically require the metadata to be broken into sub-blocks so that applications can navigate the metadata block without knowing its internal structure.

The [[Extensible Metadata Platform]] (XMP) metadata standard introduced an unofficial but now widespread "XMP Data" application extension block for including XMP data in GIF files.<ref>{{cite web |url=https://wwwimages2.adobe.com/content/dam/acom/en/devnet/xmp/pdfs/XMP%20SDK%20Release%20cc-2016-08/XMPSpecificationPart3.pdf |title=XMP Specification Part 3: Storage in Files |date=2016 |publisher=Adobe |pages=11–12 |access-date=16 August 2018 |archive-date=25 February 2018 |archive-url=https://web.archive.org/web/20180225154501/https://wwwimages2.adobe.com/content/dam/acom/en/devnet/xmp/pdfs/XMP%20SDK%20Release%20cc-2016-08/XMPSpecificationPart3.pdf |url-status=live }}</ref> Since the XMP data is encoded using [[UTF-8]] without NUL characters, there are no 0 bytes in the data. Rather than break the data into formal sub-blocks, the extension block terminates with a "magic trailer" that routes any application treating the data as sub-blocks to a final 0 byte that terminates the sub-block chain.