[ENH] Extend date time information to include optional UTC syntax, warn about FIF requirements

src/02-common-principles.md

@@ -459,7 +459,7 @@ pairs. JSON files MUST be in UTF-8 encoding. Extensive documentation of the
 format can be found here: [http://json.org/](http://json.org/). Several editors
 have built-in support for JSON syntax highlighting that aids manual creation of
 such files. An online editor for JSON with built-in validation is available at:
-[http://jsoneditoronline.org](http://jsoneditoronline.org). 
+[http://jsoneditoronline.org](http://jsoneditoronline.org).
 It is RECOMMENDED that keys in a JSON file are written in [CamelCase](https://en.wikipedia.org/wiki/Camel_case)
 with the first letter in upper case (e.g., `SamplingFrequency`, not
 `samplingFrequency`). Note however, when a JSON file is used as an accompanying
@@ -542,14 +542,25 @@ Describing dates and timestamps:
 -   Date time information MUST be expressed in the following format
     `YYYY-MM-DDThh:mm:ss[.000000]` (year, month, day, hour (24h), minute,
     second, and optionally fractional second).
-    This is equivalent to the RFC3339 "date-time" format, time zone is always
-    assumed as local time).
+    This is almost equivalent to the [RFC3339](https://tools.ietf.org/html/rfc3339)
+    "date-time" format, with the exception that in BIDS, time zone is always
+    assumed as local time.
+    The RFC3339 `Z` syntax to indicate UTC or the RFC3339 "offset" syntax are not
+    supported.
     No specific precision is required for fractional seconds, but the precision
     SHOULD be consistent across the dataset.
-    For example `2009-06-15T13:45:30`
+    For example `2009-06-15T13:45:30`.
 
 -   Time stamp information MUST be expressed in the following format:
-    `13:45:30[.000000]`
+    `hh:mm:ss[.000000]`
+    For example `13:45:30`.
+
+-   Note that depending on local REB/IRB ethics board policy, Date time information
+    does not need to be fully detailed.
+    For example, it is permissible to set the time to `00:00:00` if reporting the
+    exact recording time is undesirable.
+    However, for privacy protection reasons, it it generally RECOMMENDED to shift
+    dates, as described below.
 
 -   Dates can be shifted by a random number of days for privacy protection
     reasons.
@@ -559,6 +570,11 @@ Describing dates and timestamps:
     within each subject to maintain the interval information.
     For example: `1867-06-15T13:45:30`
 
+-   WARNING: The Neuromag/Elekta/MEGIN file format for MEG (`.fif`) does *not*
+    support recording dates earlier than `1902` roughly.
+    See [MEG-file-formats](./99-appendices/06-meg-file-formats.md#recording-dates-in-fif-files)
+    for more information.
+
 -   Age SHOULD be given as the number of years since birth at the time of
     scanning (or first scan in case of multi session datasets). Using higher
     accuracy (weeks) should in general be avoided due to privacy protection,

src/04-modality-specific-files/02-magnetoencephalography.md

@@ -170,12 +170,8 @@ Example:
 ```
 
 Note that the date and time information SHOULD be stored in the Study key file
-(`scans.tsv`), see [Scans file](../03-modality-agnostic-files.md#scans-file). As
-it is indicated there, date time information MUST be expressed in the following
-format `YYYY-MM-DDThh:mm:ss`
-([ISO8601](https://en.wikipedia.org/wiki/ISO_8601) date-time format). For
-example: 2009-06-15T13:45:30. It does not need to be fully detailed, depending
-on local REB/IRB ethics board policy.
+(`scans.tsv`), see [Scans file](../03-modality-agnostic-files.md#scans-file).
+Date time information MUST be expressed as indicated in [Units](../02-common-principles.md#units)
 
 ## Channels description (`*_channels.tsv`)
 

src/04-modality-specific-files/03-electroencephalography.md

@@ -183,12 +183,8 @@ Example:
 ```
 
 Note that the date and time information SHOULD be stored in the Study key file
-([`scans.tsv`](../03-modality-agnostic-files.md#scans-file)). As it is
-indicated there, date time information MUST be expressed in the following
-format `YYYY-MM-DDThh:mm:ss`
-([ISO8601](https://en.wikipedia.org/wiki/ISO_8601) date-time format). For
-example: 2009-06-15T13:45:30. It does not need to be fully detailed, depending
-on local REB/IRB ethics board policy.
+([`scans.tsv`](../03-modality-agnostic-files.md#scans-file)).
+Date time information MUST be expressed as indicated in [Units](../02-common-principles.md#units)
 
 ## Channels description (`*_channels.tsv`)
 

src/04-modality-specific-files/04-intracranial-electroencephalography.md

@@ -200,12 +200,8 @@ Example:
 ```
 
 Note that the date and time information SHOULD be stored in the Study key file
-([`scans.tsv`](../03-modality-agnostic-files.md#scans-file)). As it is indicated
-there, date time information MUST be expressed in the following format
-`YYYY-MM-DDThh:mm:ss`
-([ISO8601](https://en.wikipedia.org/wiki/ISO_8601) date-time format). For
-example: 2009-06-15T13:45:30. It does not need to be fully detailed, depending
-on local REB/IRB ethics board policy.
+([`scans.tsv`](../03-modality-agnostic-files.md#scans-file)).
+Date time information MUST be expressed as indicated in [Units](../02-common-principles.md#units)
 
 ## Channels description (`*_channels.tsv`)
 
@@ -339,7 +335,7 @@ For example:
 The order of the required columns in the `*_electrodes.tsv` file MUST be as
 listed below.
 
-MUST be present:                                                   
+MUST be present:
 
 | Column name  | Definition                                                                                                                                 |
 | ---------------------- | -------------------------------------------------------------------------------------------------------------------------------- |

src/99-appendices/06-meg-file-formats.md

@@ -118,6 +118,16 @@ More information can be found under the following links:
 -   [Neuromag/Elekta/MEGIN data organization](http://www.fieldtriptoolbox.org/getting_started/neuromag)
 -   [BabyMEG](http://www.fieldtriptoolbox.org/getting_started/babysquid)
 
+### recording dates in `.fif` files
+
+It is important to note that recording dates in `.fif` files are represented
+as `int32` format seconds since (or before) [*the Epoch*](https://en.wikipedia.org/wiki/Unix_time)
+(`1970-01-01T00:00:00.000000` UTC).
+Integers in `int32` format can encode values from -2,147,483,647 to +2,147,483,647.
+Due to this representation, the Neuromag/Elekta/MEGIN file format for MEG (`.fif`) does *not*
+support recording dates earlier than `1901-12-13T08:45:53.000000` UTC or later than
+`2038-01-19T03:14:07.000000` UTC.
+
 ## BTi/4D neuroimaging
 
 Each experimental run on a 4D neuroimaging/BTi system results in a folder