Computes the common prefix that is shared by all rows in @completion
that start with @key.
If no row matches @key, %NULL will be returned.
Note that a text column must have been set for this function to work,
see [method@Gtk.EntryCompletion.set_text_column] for details.
Computes the common prefix that is shared by all rows in @completion that start with @key.
If no row matches @key, %NULL will be returned. Note that a text column must have been set for this function to work, see [method@Gtk.EntryCompletion.set_text_column] for details.