Purpose

This post-function can be used for replacing a substring in the content of another field. The replacing string is defined by the content of another field. You can implement this same behavior using more advanced features like Copy parsed text to a field or Format field value post-functions.

Example: Replace reporter with current user if he does not belong to the administrator project role

If reporter doesn't belong to role Administrators, then replace the username of the Reporter in the issue Description with the one of the Current User: 

Note that:

•  %{00006} is field code for Reporter

Once configured, the post-function looks like this: