What Regex syntax is used to specify include/exclude for clamscan

I just installed clamav on my linux system.

I intend to do a manual scan of the whole system from root (/). But there are directories I know should be skipped (e.g. /proc, /sys, /dev).

The clamscan online documentation only gives an abbreviated list of options. clamscan --help gives much more but it ONLY says:

--exclude=REGEX                      Don't scan file names matching REGEX
--exclude-dir=REGEX                  Don't scan directories matching REGEX
--include=REGEX                      Only scan file names matching REGEX
--include-dir=REGEX                  Only scan directories matching REGEX

Nowhere can I find any description of the specific REGEX syntax to use.

In particular I want to know if I should use grep basic or extended regex syntax or perhaps some other dialect.

I also found a post where someone was using --exclude to exclude directories instead of --exclude-dir and would like to know if that should work.