[EDF to BIDS revision] Unclear explanation about how to extract Startime and Stoptime metadata

[celprov]

hcph-sops/docs/data-management/edf-to-bids.md

Lines 51 to 83 in c370b04

	We then search for messages signaling the start and stop run events.
	These events are stored in the JSON sidecar file annotating our `_eyetrack.tsv.gz` file.
	In our *Psychopy* experiment files, we configure messages be sent to the ET at these events.
	The message changes a little with the RSfMRI experiment, but are usually like `hello <taskname>` and `bye <taskname>`, which are stored in the variables `message_first_trigger` and `message_last_trigger` variables, respectively.
	In the last line, we clean up these used-up lines from the dataframe.
	``` Python
	# Find Start time
	start_rows = messages.trialid.str.contains(
	message_first_trigger, case=False, regex=True
	)
	stop_rows = messages.trialid.str.contains(
	message_last_trigger, case=False, regex=True
	)
	# Extract calibration headers
	_cal_hdr = messages.trialid.str.startswith("!CAL")
	calibration = messages[_cal_hdr]
	messages = messages.drop(messages.index[_cal_hdr])
	# Pick the LAST of the start messages
	metadata["StartTime"] = (
	int(messages[start_rows].trialid_time.values[-1])
	if start_rows.any()
	else None
	)
	# Pick the FIRST of the stop messages
	metadata["StopTime"] = (
	int(messages[stop_rows].trialid_time.values[0])
	if stop_rows.any()
	else None
	)

• L52: Looking at a _eyetrack_physio.json, it is not clear to me what those events described in the JSON are
• L54: how are the message_first_trigger and message_last_trigger initialized (probably related to [EDF to BIDS revision] Add code snippet about how to call the script for EDF to BIDS conversion #455)
• L71, L78: why do we extract the last start message and the first stop message?