Features used to implement the example

• Calculated Number Field

Example: Number of open subtasks

Count the number of subtasks, which are open (in status category  To Do or In Progress).

A valid configuration for this Calculated Text Field:

Text to be parsed

• count(filterByPredicate(subtasks(), ^%{00144} = "To Do" OR ^%{00144} = "In Progress"))

Note that:

• %{00144} is the field code for Status Category
• The ^ is used for referencing the field values of the issue list l - in this case subtasks(). Without, the field codes would reference to the current issue.
  [Schema for function filterByPredicate(issue list l, boolean expression predicate)]

Once configured and added to an issue screen, the result will look like this: