anchor.diff:  ===== Calendar intervals
   
   Calendar-aware intervals are configured with the `calendar_interval` parameter.
  -Calendar intervals can only be specified in "singular" quantities of the unit
  -(`1d`, `1M`, etc). Multiples, such as `2d`, are not supported and will throw an exception.
  -
  -The accepted units for calendar intervals are:
  -
  -minute (`1m`) ::
  +You can specify calendar intervals using the unit name, such as `month`, or as a
  +single unit quantity, such as `1M`. For example, `day` and `1d` are equivalent.
  +Multiple quantities, such as `2d`, are not supported.
  +
  +The accepted calendar intervals are:
  +
  +`minute`, `1m` ::
   
   All minutes begin at 00 seconds.
   One minute is the interval between 00 seconds of the first minute and 00
  -seconds of the following minute in the specified timezone, compensating for any
  +seconds of the following minute in the specified time zone, compensating for any
   intervening leap seconds, so that the number of minutes and seconds past the
   hour is the same at the start and end.
   
  -hour (`1h`) ::
  +`hour`, `1h` ::
   
   All hours begin at 00 minutes and 00 seconds.
   One hour (1h) is the interval between 00:00 minutes of the first hour and 00:00
  -minutes of the following hour in the specified timezone, compensating for any
  +minutes of the following hour in the specified time zone, compensating for any
   intervening leap seconds, so that the number of minutes and seconds past the hour
   is the same at the start and end.
   
  -day (`1d`) ::
  +`day`, `1d` ::
   
   All days begin at the earliest possible time, which is usually 00:00:00
   (midnight).
   One day (1d) is the interval between the start of the day and the start of
  -of the following day in the specified timezone, compensating for any intervening
  +of the following day in the specified time zone, compensating for any intervening
   time changes.
   
  -week (`1w`) ::
  +`week`, `1w` ::
   
   One week is the interval between the start day_of_week:hour:minute:second
   and the same day of the week and time of the following week in the specified
  -timezone.
  -
  -month (`1M`) ::
  +time zone.
  +
  +`month`, `1M` ::
   
   One month is the interval between the start day of the month and time of
   day and the same day of the month and time of the following month in the specified
  -timezone, so that the day of the month and time of day are the same at the start
  +time zone, so that the day of the month and time of day are the same at the start
   and end.
   
  -quarter (`1q`) ::
  -
  -One quarter (1q) is the interval between the start day of the month and
  +`quarter`, `1q` ::
  +
  +One quarter is the interval between the start day of the month and
   time of day and the same day of the month and time of day three months later,
   so that the day of the month and time of day are the same at the start and end. +
   
  -year (`1y`) ::
  -
  -One year (1y) is the interval between the start day of the month and time of
  +`year`, `1y` ::
  +
  +One year is the interval between the start day of the month and time of
   day and the same day of the month and time of day the following year in the
  -specified timezone, so that the date and time are the same at the start and end. +
  +specified time zone, so that the date and time are the same at the start and end. +
   
   [[calendar_interval_examples]]
   ===== Calendar interval examples
  
positive.code: data requires special support because time-based intervals are not always a
  fixed length.
  
  [[calendar_and_fixed_intervals]]
  ==== Calendar and fixed intervals
  
  
negative.code: 
  The accepted units for fixed intervals are:
  
  milliseconds (`ms`) ::
  A single millisecond. This is a very, very small interval.
  
  seconds (`s`) ::
  Defined as 1000 milliseconds each.
  
  minutes (`m`) ::
  Defined as 60 seconds each (60,000 milliseconds).
  All minutes begin at 00 seconds.
  
  hours (`h`) ::
  Defined as 60 minutes each (3,600,000 milliseconds).
  All hours begin at 00 minutes and 00 seconds.
  
  days (`d`) ::
  Defined as 24 hours (86,400,000 milliseconds).
  All days begin at the earliest possible time, which is usually 00:00:00
  (midnight).
  
  [[fixed_interval_examples]]
  ===== Fixed interval examples
  