SEP 55: Syntax for tasks and spaced repitition cards

Djot includes a syntax for marking block content as only being relevant to specific outputs. The below snippet (were it not escaped) would not be visible unless I ran it through a ‘task’ specific parser. This feature could be used to allow for embedding various blocks within my source documents without them being rendered/exposed in the resulting published HTML.

``` =task
This is a task.
```

Examples where this could be useful:

• Extended comments/todo items within a document that would not be of interest to a reader.
• Defining spaced-repetition cards within the context of a relevant document, without that card being passed through to the HTML. This would allow for my viewing said cards either within the context of that document or separated from it for practising.
• Same as above but for task management, so that a task could be defined from within any document. This could also support a ‘status’ parameter, perhaps =task:complete, =task:inprogress, etc.