enable 'metadata-url/-path/-parent/-extractor]' by default

assign values to "private" keys to not have them appear in the
standard JSON output, while still making it easier to access them

docs/configuration.rst

@@ -253,7 +253,10 @@ Type
     * ``bool``
     * ``string``
 Default
-    `extractor.parent <extractor.*.parent_>`__
+    ``true``
+        `extractor.parent <extractor.*.parent_>`__
+    ``"_parent"``
+        otherwise
 Description
     Forward a parent's metadata to its child extractors.
 
@@ -1089,6 +1092,8 @@ extractor.*.metadata-url
 ------------------------
 Type
     ``string``
+Default
+    ``"_url"``
 Description
     Insert a file's download URL into its metadata dictionary as the given name.
 
@@ -1105,6 +1110,8 @@ extractor.*.metadata-path
 -------------------------
 Type
     ``string``
+Default
+    ``"_path"``
 Description
     Insert a reference to the current
     `PathFormat <https://github.com/mikf/gallery-dl/blob/v1.27.0/gallery_dl/path.py#L27>`__
@@ -1120,6 +1127,8 @@ extractor.*.metadata-extractor
 ------------------------------
 Type
     ``string``
+Default
+    ``"_extr"``
 Description
     Insert a reference to the current
     `Extractor <https://github.com/mikf/gallery-dl/blob/v1.27.0/gallery_dl/extractor/common.py#L28>`__
@@ -1132,6 +1141,8 @@ extractor.*.metadata-http
 -------------------------
 Type
     ``string``
+Default
+    ``null``
 Description
     Insert an ``object`` containing a file's HTTP headers and
     ``filename``, ``extension``, and ``date`` parsed from them
@@ -1148,6 +1159,8 @@ extractor.*.metadata-version
 ----------------------------
 Type
     ``string``
+Default
+    ``null``
 Description
     Insert an ``object`` containing gallery-dl's version info into
     metadata dictionaries as the given name.

docs/gallery-dl.conf

@@ -71,11 +71,11 @@
         "path-convert" : null,
         "path-extended": true,
 
-        "metadata-extractor": null,
+        "metadata-extractor": "_extr",
+        "metadata-parent"   : "_parent",
+        "metadata-path"     : "_path",
+        "metadata-url"      : "_url",
         "metadata-http"     : null,
-        "metadata-parent"   : null,
-        "metadata-path"     : null,
-        "metadata-url"      : null,
         "metadata-version"  : null,
 
         "sleep"          : 0,

gallery_dl/job.py

@@ -69,12 +69,16 @@ class Job():
         extr.log = self._wrap_logger(extr.log)
         extr.log.debug("Using %s for '%s'", extr.__class__.__name__, extr.url)
 
-        self.metadata_url = extr.config2("metadata-url", "url-metadata")
+        self.metadata_url = extr.config2(
-        self.metadata_http = extr.config2("metadata-http", "http-metadata")
+            "metadata-url", "url-metadata", "_url")
-        metadata_path = extr.config2("metadata-path", "path-metadata")
+        self.metadata_http = extr.config2(
-        metadata_version = extr.config2("metadata-version", "version-metadata")
+            "metadata-http", "http-metadata")
+        metadata_path = extr.config2(
+            "metadata-path", "path-metadata", "_path")
+        metadata_version = extr.config2(
+            "metadata-version", "version-metadata")
         metadata_extractor = extr.config2(
-            "metadata-extractor", "extractor-metadata")
+            "metadata-extractor", "extractor-metadata", "_extr")
 
         if metadata_path:
             self.kwdict[metadata_path] = path_proxy
@@ -467,7 +471,7 @@ class DownloadJob(Job):
                 extr._parentdir = pextr._parentdir
 
             if pmeta := pextr.config2(
-                    "parent-metadata", "metadata-parent", parent):
+                    "parent-metadata", "metadata-parent", parent or "_parent"):
                 if isinstance(pmeta, str):
                     data = self.kwdict.copy()
                     if kwdict: