In constructor columnName is passed as parameter.
public esQueryItem (
esDynamicQuery query,
string columnName
)
However I wasn't able to fint the property ColumnName or something similar.
After some time I understood, that they use implicit operator string
public static implicit operator string (
esQueryItem item
)
which does the magic.
However the explicit read-Only property ColumnName will be useful.
By the way the help shows 2 different operators as the same