Column expressions that match TEXT or CDATA nodes must return the
contents of the nodes themselves, not the content of non-existing
children (i.e. the empty string).

Author: Markus Winand
Reported-by: Markus Winand
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/0684A598-002C-42A2-AE12-F024A324EAE4@winand.at