All Sieve scripts are represented in UTF-8, but messages may involve a number of character sets. In order for comparisons to work across character sets, implementations SHOULD implement the following behavior:
Implementations decode header charsets to UTF-8. Two strings are considered equal if their UTF-8 representations are identical. Implementations should decode charsets represented in the forms specified by [MIME] for both message headers and bodies. Implementations must be capable of decoding US-ASCII, ISO-8859-1, the ASCII subset of ISO-8859-* character sets, and UTF-8.
If implementations fail to support the above behavior, they MUST conform to the following:
No two strings can be considered equal if one contains octets greater than 127.
In order to allow for language-independent, case-independent matches, the match type may be coupled with a comparator name. Comparators are described for [ACAP]; a registry is defined for ACAP, and this specification uses that registry.
ACAP defines multiple comparator types. Only equality types are used in this specification.
All implementations MUST support the "i;octet" comparator (simply compares octets) and the "i;ascii-casemap" comparator (which treats uppercase and lowercase characters in the ASCII subset of UTF-8 as the same). If left unspecified, the default is "i;ascii-casemap".
Some comparators may not be usable with substring matches; that is, they may only work with ":is". It is an error to try and use a comparator with ":matches" or ":contains" that is not compatible with it.
A comparator is specified by the ":comparator" option with commands that support matching. This option is followed by a string providing the name of the comparator to be used. For convenience, the syntax of a comparator is abbreviated to "COMPARATOR", and (repeated in several tests) is as follows:
":comparator" <comparator-name: string>
So in this example,
if header :contains :comparator "i;octet" "Subject"
"MAKE MONEY FAST" {
discard;
}
would discard any message with subjects like "You can MAKE MONEY FAST", but not "You can Make Money Fast", since the comparator used is case-sensitive.
Comparators other than i;octet and i;ascii-casemap must be declared with require, as they are extensions. If a comparator declared with require is not known, it is an error, and execution fails. If the comparator is not declared with require, it is also an error, even if the comparator is supported. (See 2.10.5.)
Both ":matches" and ":contains" match types are compatible with the "i;octet" and "i;ascii-casemap" comparators and may be used with them.
It is an error to give more than one of these arguments to a given command.