Nutshell

This is a non-standard implementation extending JSON pointers:

https://tools.ietf.org/html/draft-ietf-appsawg-json-pointer-04

It allows you to reference parts of a JSON document from within the same document from within a sub-string.

In other words, JSON Pointers can handle resolving things like:

{
    "a": "foo",
    "b": "/a"
}

However, this proposes a new variable spec requiring an additional template:

{
    "a": "foo",
    "b": "{{/a}}"
}

By using a template, we can replace sub-strings:

{
    "a": "foo",
    "b": "{{/a}}, bar!"
}

Example

The motivation for this is to try and share settings between the front-end and back-end of an application, settings within the same JSON document can reference each other to prevent repetition. Consider the following document:

{
    "USERNAME_REGEX": "[a-zA-Z0-9._-]{3,30}",
    "USERNAMES_REGEX": "{{/USERNAME_REGEX}}(?:,{{/USERNAME_REGEX}})*",
    "FILE_ID_REGEX": "{{/USERNAME_REGEX}}:\\d+"
}

After de-referencing the variables, you get:

{
    "USERNAME_REGEX": "[a-zA-Z0-9._-]{3,30}",
    "USERNAMES_REGEX": "[a-zA-Z0-9._-]{3,30}(?:,[a-zA-Z0-9._-]{3,30})*",
    "FILE_ID_REGEX": "[a-zA-Z0-9._-]{3,30}:\\d+"
}

The original document is more readable and revisions to the first value only require changing one line.