On Thu, Jul 30, 2015 at 1:46 PM, Alexander Walters firstname.lastname@example.org wrote:
'.is_dst' of one spelling or another is unambiguous;
.. and is "clearly" defined by the POSIX standard as follows:
"A positive or 0 value for tm_isdst shall cause mktime() to presume initially that Daylight Savings Time, respectively, is or is not in effect for the specified time. A negative value for tm_isdst shall cause mktime() to attempt to determine whether Daylight Savings Time is in effect for the specified time." 
Call me when you find two people who can agree on what this means.