anchor.diff:  If this attribute is not specified, the link name will fall back to **Raw URL**.
   
   The link name will be incorporated into the click-tracked link and will be tracked in engagement events.
  +
  +### Unsubscribe Links
  +
  +It is possible to indicate that a link in your content be used to generate an unsubscribe event from SparkPost. This is done with the **data-msys-unsubscribe** custom attribute. For example:
  +
  +```
  +<a href="http://www.example.com/unsub_handler?id=1234" data-msys-unsubscribe="1">Unsubscribe</a>
  +```
  +
  +More information can be found [here](https://support.sparkpost.com/customer/portal/articles/1929894-setting-up-unsubscribe-links).
  +
  +### Per-link Disabling of Click Tracking
  +
  +When click-tracking is enabled for a transmission individual links can be skipped using the **data-msys-clicktrack** custom attribute. For example:
  +
  +```
  +<a href="http://www.example.com/" data-msys-clicktrack="0">Click</a>
  +```
  +
  +
  +### Custom Link Sub-Paths
  +
  +It is possible to add a custom sub-path to a tracked URL using the **data-msys-sublink** custom attribute. For example:
  +
  +```
  +<a href="http://www.example.com/" data-msys-sublink="custom_path">Click</a>
  +```
  +
  +The tracked link generated will look like this:
  +
  +```
  +http://<hostname>/f/custom_path/<encoded target url>
  +```
  +
  +An example of how to use **data-msys-sublink** to support iOS Universal Links in SparkPost Elite can be found [here](https://support.sparkpostelite.com/customer/en/portal/articles/2231112-ios9-universal-links-support?b_id=8730#Creating%20Universal%20Links%20in%20Templates%20&%20Sub-Pathing).
  +
  +### Link Attributes in Text Parts
  +
  +The sections above describing the **data-msys-*** link attributes all show HTML `<a>` tag examples. However it is also possible to specify all of the same custom attributes for links in the `text` part of a message using a double-square-bracket notation. For example:
  +
  +```
  +http://www.example.com[[data-msys-clicktrack="0"]]
  +```
   
   ### Substitutions Syntax Examples
   
  
positive.code:             {
                "name": "Sparkle Ponies",
                "key_label": "API Key for Sparkle Ponies Subaccount",
                "key_grants": ["smtp/inject", "sending_domains/manage", "message_events/view", "suppression_lists/manage"]
              }
  
  + Response 200 (application/json)
  
negative.code: 
  ### Create new subaccount [POST]
  
  Provisions a new subaccount and an initial subaccount API key. Subaccount API keys are only allowed very specific grants, which are limited to: `smtp/inject`, `sending_domains/manage`, `tracking_domains/view`, `tracking_domains/manage`, `message_events/view`, `suppression_lists/manage`, `transmissions/view`, and `transmissions/modify`.
  
  Subaccounts are allowed to send mail using the SMTP protocol or Transmissions API, retrieve sending statistics via the Message Events API, manage their Sending Domains, manage their Suppression List.
  
  