The TextBundle file format aims to provide a more seamless user expericence when exchanging Markdown files between sandboxed applications.
Sandboxing is required for all apps available on the Mac and iOS app store, in order to grant users a high level of data security. Sandboxed apps are only permitted access to files explicitly provided by the user - for example Markdown text files. When working with different Markdown applications, sandboxing can cause inconveniences for the user.
An example: Markdown files may contain references to external images. When sending such a file from a Markdown editor to a previewer, users will have to explicitly permit access to every single image file.
This is where TextBundle comes in. TextBundle brings convenience back - by bundling the Markdown text and all referenced images into a single file. Supporting applications can just exchange TextBundles without asking for additional permissions. Beyond being a simple container, TextBundle includes a standard to transfer additional information - to open up new possibilites for future integration.
These guys are doing God’s work. You can read more about the spec here. This is exciting.