HFS: File masks
What is it?
A file mask denotes a set of files. It is usually something like this: *.jpg;*.gif. This example denotes any jpeg and gif files. Remember that the characters used in filenames are not case sensitive: so *.jpg and *.JPG refer to exactly the same set of files.
How does it work?
The example above shows a double file mask. It has two atoms separated by the semicolon: *.jpg and *.gif. The semicolon is used to merge multiple masks: it is a special character. There are only three special characters in file masks: ; * and ?.
The star (*)
The star (also called "asterisk") stands for any string of characters. If the mask contains only the star, it matches ANY file.
If you put an A before the star A*, it matches any file starting with an A.
If you put an A after the star *A, it matches any file ending with an A.
A*B matches any file starting with an A and ending with a B. The example above shows *.jpg : it matches any file ending with .jpg (that is, jpeg images). jpeg files are relatively unusual because they sometimes end with .jpeg and more rarely with .jpe . (The part of a filename that comes after the period is called the file "extension", and is normally limited to three characters.) You could use the mask .jp* to match all types of jpeg files.
The star also matches the null string: A*.jpg matches files like A1.jpg , Adfgg.jpg but also A.jpg.
The question mark (?)
This stands for a single character. Something like A?B matches any filename that is three characters long and starts with an A and ends with a B. The length is fixed to three characters because ? can be replaced by only one character. Thus the ? does not match the null string as the * does.
Inverting the logic (\)
So you want to hide filetypes, instead of showing specific filetypes?
Insert a backslash \ before *.ext to achieve opposite logic with the filter, and hide the filetypes you do not want visible to users. E.g \*.db;*.ini