Checks whether day basis conventions are valid. Supported day basis
conventions are documented in year_frac()
Usage
is_valid_day_basis(day_basis)
Arguments
day_basis
A character vector of day basis conventions.
Value
will return TRUE for day_basis elements that are any of the
following: 30/360, 30/360us, 30e/360,
30e/360isda, 30e+/360, act/360, act/365 and
act/actisda. Otherwise will return FALSE