I tried to use such rule:
:0 B
* Something[[:space:]]+whatever
but it doesn't work.
When I change [[:space:]] to literal space character:
:0 B
* Something +whatever
it works.
It also works in case of:
:0 B
* Something[ ]+whatever
I must be doing something wrong, but can't really find it. Any hints?
What about just adding the white space characters in a class you want to match:
[ \t\r\n]
matches a space, tab, carriage return and line feed.
There are of course more white space chars, but these are the most commonly used.