Hello,.

I want  to ask about is_timesheet in odoo10, in previous version (v.9) the field is_timesheet in account.analytic.line is only boolean, but in odoo10 it turn become readonly. So everytime I create a timesheet the field will not change to true or false.
As far I know, is_timesheet field is used in expense too. in the expense this field will have value 'false' to make sure it not read as a timesheet. 
My question, why now in odoo10 'is_timesheet' field is turn to readonly? 
anyone can explain to me more? or can give me recomedation to read more about it.
Thanks.