You can store notes without containers at all.
Open Preferences -> General -> Containers and select "None". Notes will be stored in plain text, Markdown or RTF.
TextBundle – file format aims to provide a more seamless user experience when exchanging plain text files, like Markdown or RTF, between applications. http://textbundle.org
File extension – .textbundle
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.
Encrypted Text Bundle
Encrypted Text Bundle used for notes encryption? What is it?
Encrypted Text Bundle is Text Pack (zipped Text Bundle), but encrypted with RNCryptor.
File extension – .etp
The RNCryptor data format is cross-platform and there are many implementations. Under the hood we have:
Password stretching with PBKDF2