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.