'iso8601' => ["!Y-m-d\TH:i:s", "Y-m-d\TH:i:s\Z" ], // NOTE: ISO 8601 dates require special input processing because of varying formats for timezone offsets
'iso8601m' => ["!Y-m-d\TH:i:s.u", "Y-m-d\TH:i:s.u\Z" ], // NOTE: ISO 8601 dates require special input processing because of varying formats for timezone offsets
'microtime' => ["U.u", "0.u00 U" ], // NOTE: the actual input format at the user level matches the output format; pre-processing is required for PHP not to fail
'http' => ["!D, d M Y H:i:s \G\M\T", "D, d M Y H:i:s \G\M\T"],