Docs: example for writing blend file libraries

doc/python_api/examples/bpy.types.BlendDataLibraries.write.py

@@ -0,0 +1,18 @@
+import bpy
+
+filepath = "//new_library.blend"
+
+# write selected objects and their data to a blend file
+data_blocks = set(bpy.context.selected_objects)
+bpy.data.libraries.write(filepath, data_blocks)
+
+
+# write all meshes starting with a capital letter and
+# set them with fake-user enabled so they aren't lost on re-saving
+data_blocks = {mesh for mesh in bpy.data.meshes if mesh.name[:1].isupper()}
+bpy.data.libraries.write(filepath, data_blocks, fake_user=True)
+
+
+# write all materials, textures and node groups to a library
+data_blocks = {*bpy.data.materials, *bpy.data.textures, *bpy.data.node_groups}
+bpy.data.libraries.write(filepath, data_blocks)