It would certainly prove handy for the GTK's file-selection dialogues to
support file-search and -selecting based upon keyboard input into the
dialog. Suppose that one has spawned an open dialog in a directory in which
numerous files reside; it would be very nice for the file-selection dialog
to scroll around in the file list based upon what a user types.

Example:

File list
aaaa
aaba
aabb

Type 'a'; first 'aaaa' becomes selected.
Type 'a'; first 'aaaa' remains selected.
Type 'b'; second 'aaba' becomes selected.
Type 'b'; third 'aabb' becomes selected.