In http://microformats.org/wiki/value-class-pattern#microformats2_parsers

Add:

• if a dt-* property has a time but lacks a timezone
• then it adopts the timezone of the most recently seen dt-* property with a timezone in that microformat.
  • if no previous dt-* properties have a timezone,
  • then it adopts its timezone from the next dt-* property with a timezone seen in that microformat.
  • otherwise it simply has a floating time (without explicit timezone).

Use-case: https://indieweb.org/This_Week_in_Google where timezone is specified explicitly on the dt-start but not the dt-end.

http://pin13.net/mf2/?url=https://indieweb.org/This_Week_in_Google provides (partial result)

"start": [
"2014-09-11 13:30-0700"
],
"end": [
"2014-09-11T15:30"
]

Whereas it should say:

"start": [
"2014-09-11 13:30-0700"
],
"end": [
"2014-09-11 15:30-0700"
]

(note the "T" to " " change in separator for the dt-end property parsed result is already resolved by http://microformats.org/wiki/microformats2-parsing-issues#parsing_a_dt-_property )