Fix: EBNF for sources was deleted (#3562, PR #3563)

environment.py

@@ -56,6 +56,32 @@ def env() -> Mapping[str, Optional[str]]:
         #
         # The first catalog listed is the default catalog.
         #
+        # A source represents a TDR dataset, TDR snapshot, or canned staging
+        # area to index. Each source is a string matching the following EBNF grammar:
+        #
+        # source = TDR source | canned source ;
+        #
+        # TDR source = 'tdr:', Google Cloud project name,
+        #              ':', ( 'dataset' | 'snapshot' ),
+        #              '/', TDR dataset or snapshot name,
+        #              ':', [ UUID prefix [ '/', Partition prefix length ] ] ;
+        #
+        # canned source = 'https://github.com',
+        #                 '/', owner,
+        #                 '/', repo,
+        #                 '/tree/', ref,
+        #                 ['/', path] ;
+        #                 ':', [ UUID prefix [ '/', Partition prefix length ] ] ;
+        #
+        # `ref` can be a branch, tag, or commit SHA. If `ref` contains special
+        # characters like `/`, '?` or `#` they must be URL-encoded.
+        #
+        # Examples:
+        #
+        # tdr:broad-jade-dev-data:snapshot/hca_mvp:2
+        # tdr:broad-jade-dev-data:dataset/hca_mvp:2/1
+        # https://github.com/HumanCellAtlas/schema-test-data/tree/de355ca/tests:2
+        #
         'AZUL_CATALOGS': None,
 
         # The Account ID number for AWS