Classes are selected by filter elements in a way similar to if expressions. We call if and on constructs ``selectors''.
Selectors are placed between the parameters of a class and its body. Filter elements begin with the keyword on, followed by the optional list of filter element parameters, in parentheses.
Example:
class
on (dst 209.10.41.242)
on (dst 199.183.24.194);
This is actually a shortcut notation of
on element params
Also, the filter can be specified along with the element.
Example:
class
on tcindex(mask 0) element (0);
is equivalent to
tcindex(mask 0) {
class
on element(0);
}
The number of a filter element can be explicitly set by including it among the parameters. (Note: most filter elements require numbers to be set this way. The only exception is route, which does not use element numbers at all.)
Example:
on (0x2e);