wks.col2.edit=
1. Checkbox 
2. Dropdown List with fixed entries
3. Combo box, dropdown list but user can enter new entries.

E.g. set column B as categorical.
Run wks.col2.edit=2, then click a cell, you can choose a category entry from dropdown list.
Run wks.col2.edit=3 and then click a cell, you can either choose a category from dropdown list or add a new category.

Click Any cell in column B, a dropdown list will show with filled categories.