When to use \ to escape operators in square brackets?

[dharmilshah99]

The . operator doesn't seem to need escaping in [.] if we just want to match ..

What operators are treated as regular characters in square brackets? Is there any documentation for this?

[ymherklotz]

There is quite good documentation of flex in their man page:

man 1 flex

Or you can also see it here: http://dinosaur.compilertools.net/flex/manpage.html

It says the following:

Note that inside of a character class, all regular expression operators lose their special meaning except escape ('\') and the character class operators, '-', ']', and, at the beginning of the class, '^'.

[dharmilshah99]

This was really helpful. Thanks!