[ENH] events.tsv should be sorted by onset values

src/modality-specific-files/task-events.md

@@ -42,6 +42,8 @@ and a guide for using macros can be found at
 -->
 {{ MACROS___make_columns_table("task.TaskEvents") }}
 
+The content of  `events.tsv` files SHOULD be sorted by values in the `onset` column.
+
 Note for MRI data:
 If any acquired scans have been discarded before forming the imaging data file,
 ensure that an `onset` of 0 corresponds to the time the first image was stored.

src/schema/rules/checks/events.yaml

@@ -27,3 +27,15 @@ StimulusFileMissing:
     - columns.stim_file != null
   checks:
     - exists(columns.stim_file, "stimuli") == length(columns.stim_file) - count(columns.stim_file, "n/a")
+
+SortedOnsets:
+  issue:
+    code: EVENT_ONSET_ORDER
+    message: |
+      The onset column in events.tsv files should be sorted.
+    level: warning
+  selectors:
+    - suffix == "events"
+    - extension == ".tsv"
+  checks:
+    - sorted(columns.onset) == columns.onset