<item href="/path to file (in your map)/file name.xdb#xpointer(/AmbientLight)">
and then write a script. It seems to work fine when I specify it in map.xdb. If I put <item href="/path to file (in your map)/file name.xdb#xpointer(/AmbientLight)"> in the first place, that lighting will be applied initially. But I can't figure out what to do next.
Added 6 minutes later
:smile03: :smile03: :smile03: :smile03: :smile03: Hooray! The editor seems to be forgetful, so I had to copy the lighting twice.
Thank you all!