Branden suggested I send some examples. So, here they are:
> <arch>:
> '[' '!'? <arch-name> (',' <arch-name>)* ']';
[alpha, sparce]
[!i386, hurd-i386]
> <feature>:
> '{' <arch-feature> (';' <arch-feature>)* '};
{i386: mmx, sse}
{i386: mmx, !sse; sparc: 64-bit-kernel}
> <version>:
> '(' <verop> <version-string> (',' <verop> <version-string>)* ')';
(= 1.2.3)
(>= 1.2.0, <= 1.2.3)
(>= 1.2, <= 1.5, != 1.3.7)
