How does one implement a multi-field checkbox in new-style Python toolboxes?

[MarkosKapes]

I'm trying to implement a new-style toolbox that allows me to introspect a feature and check which fields to draw data from. This was straightforward in the old-style toolboxes, something along the lines of:

        param0 = arcpy.Parameter( displayName="Input Features", name="in_features", datatype="GPFeatureLayer", parameterType="Required", direction="Input")

However, when I try that in a new toolbox, the control won't display that parameter..... any help would be appreciated.

[DanPatterson_Retired]

The information and examples is limited showing only how to use it in tool validation

Parameter—Help | ArcGIS for Desktop  due note that the valueastext parameter is only for python toolboxes,  I would begin to see if your accepted defaults behave differently in conventional vs python toolboxes