With the completion of #843 we have a much more powerful fractionalEvaluation.

One problem remains:

"fractionalEvaluation": [
          "email"
          [
            "red",
            25
          ],
          [
            "blue",
            25
          ],
          [
            "green",
            25
          ],
          [
            "purple",
            25
          ]
        ]

has been replaced with:

"fractionalEvaluation": [
          {
            "var": "email"
          },
          [
            "red",
            25
          ],
          [
            "blue",
            25
          ],
          [
            "green",
            25
          ],
          [
            "purple",
            25
          ]
        ]

However, there's a problem which was not immediately apparent. "email" in the first variant is treated as a literal in our new operator: by the time our operator runs, it's difficult (impossible?) to know if the first value ("email" in this case) was the result of an expression ( "var": "myProp" ) or it was hard-coded. This means we should deprecate the old fractionalEvaluation and ignore it, and instruct people on how to properly use a new operator fractional. We can do this with a helpful log warning.

EDIT:

I've maintained the old behavior offractionalEvaluation, and added a deprecation log warning, and moved the new implementation to fractional.

The deprecation warning log message points directly to the migration instructions in the web-docs.