I wanted to creat a multi select combo box using python tkinter.ttk and needed to understand ttk widgets

I used the code below to get something that works, but I really want to understand how the ttk.Combobox can be controlled better. This question(How to know all style options of a ttk widget?) shows how to print out all the styles an layout, but I would like to see the events and component structure.

import tkinter as tk
from tkinter import ttk


class MultiBox(ttk.Combobox):
    def __init__(self,window,**kwds):
        self._separator = kwds.pop('separator',None)
        self._joinChar = self._separator if self._separator is not None else ' '
        kwds["textvariable"] = self._v = kwds.pop('textvariable',tk.StringVar())
        self._v.trace('w',self.vwrite)
        self.onchange = kwds.pop('onchange',None)
        super().__init__(window,**kwds)
        self["values"] = self._values = list(kwds.pop('values',()))
        self._cv = ''

    def vwrite(self,*args):
        v = set((_ for _ in self._v.get().split(self._separator) if _ in self._values))
        cv = set((_ for _ in self._cv.split(self._separator) if _ in self._values))
        lv = v if v&cv else v.union(cv)
        self._cv = self._joinChar.join(self._vsort(lv))
        self._v.set(self._cv)
        #print(f'{v=} {cv=} {lv=} --> {self._v}')
        self["values"] = self._vsort((_ for _ in self._values if _ not in lv))
        if self.onchange: self.onchange()

    def _vsort(self,L):
        return [_[1] for _ in sorted((self._values.index(_),_) for _ in L)]

    @property
    def value(self):
        return self._v.get()


if __name__=='__main__':
    # Creating tkinter window
    window = tk.Tk()
    window.geometry('350x270')
    # Label
    ttk.Label(window, text = "Select the Month :",
            font = ("Times New Roman", 10)).grid(column = 0,
            row = 0, padx = 10, pady = 25)
    mb0 = MultiBox(window, width = 20,
                                    values=('January','February', 'March', 'April', 'May',
                                            'June', 'July', 'August', 'September', 'October',
                                            'November', 'December'),
                              )

    mb0.grid(column = 1, row = 0)

    # Shows item 1 as a default value
    mb0.current(1)

    mb1 = MultiBox(window,width=20,values='A a,B b,C c,D d,E e,F f'.split(','),separator=',')
    mb1.grid(column = 1, row = 5, pady=10)
    mb1.current(0)

    b0 = ttk.Button(window, text="Print",
                 command=lambda :print(f'mb0.value={mb0.value} mb1.value={mb1.value}')).grid(column=1, row=15, pady=5)
    b1 = ttk.Button(window, text="Quit", command=window.destroy).grid(column=1, row=20, pady=5)

    #from ttkstyopt import ttkStyOpt
    #window.after(10000, lambda : ttkStyOpt(multibox))
    window.mainloop()