The arguments start.date and end.date can be set but once they aren't and holidays
is set, start.date is defined to min(holidays) and end.date to max(holidays).
If holidays isn't set start.date is set to '1970-01-01' and end.date to '2071-01-01'.
weekdays is controversial but it is only a sequence of nonworking weekdays.
In the great majority of situations it refers to the weekend but it is also possible defining
it differently.
weekdays accepts a character sequence with lower case weekdays (
sunday, monday, thuesday, wednesday, thursday,
friday, saturday).
This argument defaults to NULL because the default intended behavior for
create.calendar returns an actual calendar, so calling create.calendar(name="xxx")
returns a actual calendar named xxx.
(for more calendars see Day Count Convention)
To define the weekend as the nonworking weekdays one could simply
use weekdays=c("saturday", "sunday").
The arguments adjust.from and adjust.to are used to adjust bizdays' arguments
from and to, respectively.
These arguments need to be adjusted when nonworking days are provided.
The default behavior, setting adjust.from=adjust.previous and adjust.to=adjust.next,
works like Excel's function NETWORKDAYS, since that is fairly used by a great number of practitioners.