add matches and source_entity to glossary

src/schema/objects/entities.yaml

@@ -422,3 +422,30 @@ tracksys:
     may be longer and more human readable.
   type: string
   format: label
+
+matches:
+  name: matches
+  display_name: matches
+  description: |
+    `matches` is used as a placeholder in BIDS filenames templates to denote that several files
+    share exactly the same sequence of entities and labels in their basename.
+
+    For example, in the following filename template
+
+    ```Text
+      <matches>_bold.nii.gz
+      <matches>_events.tsv
+      <matches>_events.json
+    ```
+
+    `<matches>` could correspond to `sub-control01_task-nback_run-1`.
+
+source_entities:
+  name: source_entities
+  display_name: source entities
+  description: |
+    `source_entities` is used as a placeholder in BIDS derivatives filenames templates.
+
+    `source_entities` MUST be the entire source filename, with the omission of
+    the source suffix and extension. One exception to this rule is filename
+    entities that are no longer relevant.