Multiple simple patterns can be separated with comma (',') as in "*.html,*.htm". Whitespace before and after a pattern is discarded, thus " *.html , *.htm " is fine also.
The most notable difference to common regular expressions is the role of the dot (fullstop, '.'). In regular expressions it denotes "any character" but in simple patterns it denotes just a dot ('.').
Wherever you can use simple patterns, you will find a checkbox "Regular Expression" below the input field. Tick that checkbox if you want to use full regular expressions for the file name pattern instead of simple patterns.
|*.txt||means any file with extension "txt", finding "TXT", "Txt" and so on just as well.|
|my*||means any file that begins with "my".|
|#*.!!!||means any file that starts with a digit and has an extension of exactly three characters.|
|*.wsdl, *.xsd||finds wsdl and xsd files.|
|*.jp?g||find JPEG image file with extension "jpg" or "jpeg" (but also jpig and alike).|