On GNU and Unix systems, a hidden file is a file whose name starts with a period. They are hidden from a regular directory listing because the user is not generally interested in them.
In speedbar, a hidden file is a file which isn't very
interesting and might prove distracting to the user. Any
uninteresting files are removed from the File display. There are
two levels of uninterest in speedbar. The first level of
uninterest are files which have no expansion method, or way of
extracting tags. The second level is any file that matches the
same pattern used for completion in find-file. This
is derived from the variable
completion-ignored-extensions.
You can toggle the display of uninteresting files from the toggle menu item ‘Show All Files’. This will display all level one hidden files. These files will be shown with a ‘?’ indicator. Level 2 hidden files will still not be shown.
Object files fall into the category of level 2 hidden files. You can determine their presence by the ‘#’ and ‘!’ file indicators. See Directory Display.