implement a 'fallback' option (closes #1770)

docs/configuration.rst

@@ -194,16 +194,6 @@ Description
     Share number of skipped downloads between parent and child extractors.
 
 
-extractor.*.url-metadata
-------------------------
-Type
-    ``string``
-Default
-    ``null``
-Description
-    Insert a file's download URL into its metadata dictionary as the given name.
-
-
 extractor.*.path-restrict
 -------------------------
 Type
@@ -507,6 +497,16 @@ Description
     `format strings`_.
 
 
+extractor.*.url-metadata
+------------------------
+Type
+    ``string``
+Default
+    ``null``
+Description
+    Insert a file's download URL into its metadata dictionary as the given name.
+
+
 extractor.*.category-transfer
 -----------------------------
 Type
@@ -671,6 +671,16 @@ Description
     will be executed as normal.
 
 
+extractor.*.fallback
+--------------------
+Type
+    ``bool``
+Default
+    ``true``
+Description
+    Use fallback download URLs when a download fails.
+
+
 extractor.*.image-range
 -----------------------
 Type

docs/gallery-dl.conf

@@ -14,6 +14,7 @@
         "retries": 4,
         "timeout": 30.0,
         "verify": true,
+        "fallback": true,
 
         "sleep": 0,
         "sleep-request": 0,