sys_CheckBoxGroup - Any way to set multiple values using JEXL input transform?

I’m attempting to use the JEXL Input Transform (labelled “Set Field” in the transform dropdown list) to assign multiple values to a check box group field. I haven’t gotten this to work. It works if I assign a string with a single keyword value (e.g. “a”) for the value the JEXL expression, but not if I try to assign multiple values. I’ve tried many different syntax variations to try and get it to take my list of values:
[“a”,“b”] (this is the supposed syntax for an array in JEXL)
(yes, I’m grasping at straws here…)

All these expressions result in the error in the console.log: “Problem evaluating expression”

I’ve also found the following during my testing:

  1. Set up the Input Transform with the JEXL expression $value (i.e. the value of the field that’s been set in the content editor window)
  2. Edit an item and select multiple choices in the checkbox field
  3. Save the item
  4. The field gets the value of only the first choice that was selected in the editor, i.e. $value evaluates only to the first choice

Has anyone been successful in getting this to work?

What is the JEXL expression name? sys_MapInputValue?

It is sys_TranslateJexlExpressionValue.