[XMLStarlet] Edit+insert elements?

Hello,

In case someone here already knows how to use the XMLStarlet application to edit KML files, I need to...

1. Check if kml/Document/name exists: If it does, edit its name; If it doesn't, insert a new element
2. Add a sibling to all LineString elements.

It looks like XMLStarlet supports it, but I don't know enough about XPath yet to figure it out.

Thank you.

Code:xml el input.kml

kml
kml/Document
kml/Document/Placemark
kml/Document/Placemark/name
kml/Document/Placemark/ExtendedData
kml/Document/Placemark/ExtendedData/Data
kml/Document/Placemark/ExtendedData/Data/value
kml/Document/Placemark/LineString
kml/Document/Placemark/LineString/coordinates