Adding support for calculated grade by fields.
Patterns of the form:

##VALUE:FIELD-PATTERN##

Supporting fields must implement interface \mod_dataform\interfaces\grading and the method get_user_values.
A valid pattern returns comma delimited list of values from the referred field.
In the formula, the pattern should be aggregated:

SUM(##VALUE:FIELD-PATTERN##)

Example 1
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With an Entry state field called 'State' the following pattern will return the sum of states of the user's entries.

SUM(##:state##)

Example 2
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With an Entry state field called 'State' the following pattern will return the number of user's entries which are in the second state (after the initial).

SUM(##2:state##)/2