completion -- a gtk:entry-completion object
key -- a string to match, normalized and case-folded
iter -- a gtk:tree-iter iterator indicating the row to match
result -- true if iter should be displayed as a possible completion for key

A callback function which decides whether the row indicated by iter matches a given key, and should be displayed as a possible completion for key. Note that key is normalized and case-folded, see the g_utf8_normalize() and g_utf8_casefold() functions. If this is not appropriate, match functions have access to the unmodified key via the (gtk:entry-text (gtk:entry-completion-entry completion)) function call. The gtk:entry-completion implementation is deprecated since 4.10. This object will be removed in GTK 5.