x++ : How edit method works, pls explain how the parameter's works

Hey can someone explain to me how edit method works, i've read some example code of this method but i can't implement it with my case. I already explained my case here :
https://community.dynamics.com/ax/f/33/p/183433/457111#457111
So, i need to modified my form's field looks just like Segmented entry in Ledger Journal, but the seperator not  going to be saved in it's table.
Also, i might need to embedded this edit method on my form-datasource-field's method. Also i can't get the edit method's parameter :
edit boolean something (boolean _set, tablename _tablename, boolean _something) --> what???
{
and what happened here??
}

THANKS!