Registration of Charset and Languages Media Features Tags
Extracted elements (11)
The 'language' tag is classified as a preference rather than a capability because most devices can attempt to process text in an unfamiliar language without catastrophic failure, unlike charsets where unknown encodings render content unprocessable.
Charset aliases MUST NOT be used in media feature expressions because feature-expression manipulation tools may convert aliases to the principal name, causing mismatches. Values SHOULD be expressed in all lowercase letters.
Language subtags are not used for comparison; language tags are always handled as a single opaque token as specified in RFC 1766.
Language tag values SHOULD be expressed in all lowercase letters even though the tags are not case-sensitive, to increase the likelihood of interoperability across implementations.
The 'charset' capability SHOULD always be indicated in conjunction with any capability to handle textual data, ensuring receivers can properly assess rendering ability.
The 'charset' media feature tag indicates a device's ability to display particular character sets. For most devices this is a capability (hard requirement), not a preference, because devices typically cannot intelligently process unknown charsets.
The 'language' media feature tag indicates a device's or user's ability to handle particular human languages. For most devices this is a preference rather than a hard requirement, and 'display' often means text-to-speech.
Registers the 'charset' media feature tag (ASN.1 OID 1.3.6.1.8.1.31) with IANA. Values are case-insensitive tokens as defined in RFC 2978 (IANA Charset Registration Procedures), compared only for equality.
Registers the 'language' media feature tag (ASN.1 OID 1.3.6.1.8.1.32) with IANA. Values are language tags as defined in RFC 1766, treated as single tokens with no subtag comparison, and compared case-insensitively.
Advertising 'charset' capability may slightly aid an attacker if a security bug exists in the display of that charset in the target environment, by confirming the device will render the attacker-chosen charset.
Advertising 'language' capability may slightly aid an attacker if a security bug exists in the display of that language in the target environment, by confirming the device will process the attacker-chosen language.