Yup, it was written from scratch. Yeah, having a flexible virtualized table certainly makes it easier to build more complex things on top (a lesson I initially learned from NSTableView/UITableView).
Currently, it's not user extendable. While it does support some IPython features (eg: Python classes that implement IPython's rich outputs also work in Scripton), ipywidgets are currently not supported.
Currently, it's not user extendable. While it does support some IPython features (eg: Python classes that implement IPython's rich outputs also work in Scripton), ipywidgets are currently not supported.