2.2.1 [W3C-PICS-Labels] General Format

V0001:

The specification states:

 A rating service may provide a generic label for any or all prefixes of a given 
 URL, but should provide only one specific label for that URL. When the specific 
 label for a document can be found, it should be used in preference to any generic 
 label. Lacking a specific label, any generic label may be substituted, but 
 preference should be given to the generic label which has the longest string. Some 
 PICS client software may impose restrictions on the use of generic labels. For 
 example, a client may choose to ignore a generic label that applies to a node in 
 the URL tree more than two levels above the node where the document is located.

All Document Modes (All Versions)

The generic label option of an initial webpage is supported, but generic label options for any subdomains are not.

V0002:

The specification states:

 Information about the document that is labeled. at quoted-ISO-date The last 
 modification date of the item to which this rating applies, at the time the rating 
 was assigned. This can serve as a less expensive, but less reliable, alternative to 
 the message integrity check (MIC) options. MIC-md5 "Base64-string" -or- md5 
 "Base64-string" A message integrity check (MIC) of the item being rated. The MD5 
 Message Digest Algorithm (see RFC1321) is used to compute the MIC. One way to 
 create this message digest is to use the RSAREF (version 2.0) software available 
 for this purpose at no charge from RSA Laboratories. See MICs and Digital 
 Signatures below.

All Document Modes (All Versions)

The syntax or validity of the actual quoted-ISO-date is not checked. The 'at' option is supported but its value is ignored.

Any "Base64-string" for a label passes through PICS rules processing normally.

V0003:

The specification states:

 Information about the label itself. 
  
 until quoted-ISO-date 
 -or- exp quoted-ISO-date 
 The date on which this rating expires.

All Document Modes (All Versions)

The "until" clause in labels is not supported.

V0004:

The specification states:

 Other information. 
  
 comment quotedname 
 Information for humans who may see the label; no associated semantics. 
  
 complete-label quotedURL 
 -or- full quotedURL 
 Dereferencing this URL returns a complete label that can be used in place of the 
 current one. The complete label has values for as many attributes as possible. This 
 is used when a short label is transmitted for performance purposes but additional 
 information is also available. When the URL is dereferenced it returns an item of 
 type application/pics-labels that contains a labellist with exactly one label. 
 extension (optional quotedURL data*) 
  
 -or- extension (mandatory quotedURL data*) 
 Future extension mechanism. To avoid duplication of extension names, each extension 
 is identified by a quotedURL. The URL can be dereferenced to get a human-readable 
 description of the extension. If the extension is optional then software which does 
 not understand the extension can simply ignore it; if the extension is mandatory 
 then software which does not understand the extension should act as though no label 
 had been supplied. Each item of data must be one of a fixed set of simple-to-parse 
 data types as specified in the detailed syntax below. See 
 http://w3.org/PICS/extensions/ to find out what extensions are currently in use.

All Document Modes (All Versions)

The data* value is supported. But if data* is enclosed in parentheses, only a single data value is supported within an extension. If more than a single value is supplied, a syntax error for the entire PICS label is returned.

C0001:

The specification states:

 Transmit-names and quoted strings are case sensitive. Option names and other tokens 
 in the BNF grammar are case insensitive.

All Document Modes (Internet Explorer 7)

Whenever transmit-name labels for a webpage do not match the label in the ratings file, an error message stating "Either the rating label on this page is invalid, or your settings have been tampered with" is returned.

All Document Modes (Internet Explorer 8 and Internet Explorer 9)

Whenever transmit-name labels for a webpage do not match the label in the ratings file, an error message stating "The rating was obtained from the webpage" is returned.

V0005:

The specification states:

 Numbers in PICS labels may be integers or fractions with no greater range or 
 precision than that provided by IEEE single-precision floating point numbers. 
 Implementors concerned about the vagaries of floating point comparisons may choose 
 to represent numbers internally as ASCII strings.

All Document Modes (Internet Explorer 7)

Numbers with a greater range or precision than that provided by IEEE single-precision floating-point numbers are supported and compared.

V0006:

The specification states:

 The multi-value syntax must be used when there is more than one value for a 
 particular category. This syntax may be used when there is exactly one value, but 
 the more compact version may also be used in that case. When there is no value, the 
 category may be omitted entirely or transmitted using the multi-value syntax.

All Document Modes (All Versions)

The multi-value syntax is recognized, but does not support multiple values for a given category. The multi-value syntax is not supported when only a single value is present. The more compact version should be used when there is only a single value.

V0007:

The specification states:

 For parsing purposes, notice that a label ends with either "ratings" or "r" 
 followed by a parenthesized list of categories and values. If this does not end the 
 label list, it is followed by either another label (possibly starting with 
 options), a new service URL (recognizable because it must be surrounded by 
 quotation marks), or an error (starting with the word "error").

All Document Modes (All Versions)

Labels can end with something other than another label, service URL, or the word "error".

V0008:

The specification states:

 Note that the content attribute uses single quotes, because the PICS label syntax 
 uses double quotes. Any of the following characters appearing within the content 
 must be escaped using SGML entities: 
         '       '           /* single quote */
         &       &           /* ampersand   */
         >       >            /* greater than */

All Document Modes (All Versions)

Ratings service names that contain an escaped ampersand (&) value are not supported.

V0009:

The specification states:

 A request for a minimal label asks that all options be omitted, unless a generic 
 label is returned, in which case the generic and for options must also be included 
 in the label. A short label includes everything that is included in a minimal 
 label, plus additional options that the server deems appropriate. A request for a 
 full label asks that as much information as possible should be sent back in the 
 label, either directly or through the use of a complete-label (or full) option, but 
 no signature-RSA-MD5 option is needed.

All Document Modes (All Versions)

Requests for labels from HTTP servers are not issued, although the labels embedded within the response header from the server are properly parsed.

V0010:

The specification states:

 The query asks the label bureau http://www.labels.org/Ratings to send a single 
 label that applies to everything in the images hierarchy at site 
 www.questionable.org. The desired label should have been created by the service 
 http://www.gcf.org/v2.5. Notice the use of %3A to represent a ":" and %2F for "/." 
 This is required for encoding characters within a URL. See RFC-1738.

All Document Modes (All Versions)

Label bureaus are not supported.

V0011:

The specification states:

 MIC-md5 or md5 
 If the label is intended to apply only to the data that was actually rated, then a 
 form of checksum (called a "message digest") can be applied to the data when the 
 label is created. The message digest is converted into US-ASCII characters using 
 MIME base-64 encoding and stored in the MIC-md5 (also called md5) field. When the 
 document is later retrieved, the same algorithm can be used to recompute the 
 message digest and the two digests can be compared. The MD5 algorithm is designed 
 so that it is extremely unlikely that the two digests will be the same if the 
 document has been tampered with in any way. 
 This technique is well-known in the cryptographic community and has been adopted by 
 the electronic mail community, where it is part of the MOSS specification. For use 
 with electronic mail, an elaborate technique is required to assure that the two 
 message digests will match, since electronic mail gateways can modify the data 
 before it is delivered (by wrapping lines, for example). We have chosen not to 
 adopt MOSS directly for PICS, largely because of this complexity. 
 Instead, we recommend the direct use of the MD5 algorithm on the source document 
 and conversion of the result to base64 encoding. This resulting string is included 
 directly in the mic-md5 (md5) label option. The MD5 algorithm and the conversion of 
 the result into US-ASCII characters is provided by the RSAREF (version 2.0) software. 
 Because PICS labels can be embedded inside of the documents they label, care must 
 be taken to ensure that the message digest is computed excluding all PICS labels in 
 the document. For HTML documents, this means that the digest must be computed after 
 removing all META elements that include PICS labels (and any whitespace immediately 
 following the end of each of these meta elements).

All Document Modes (All Versions)

The md5 label option is not supported. When this option is specified, the contents of the option are ignored.

V0012:

The specification states:

 When the client receives a label and wants to verify the signature it takes the 
 label it received and converts it back into the same special form in which it was 
 originally signed. The client recomputes the message digest on this special form. 
 It also takes the contents of the signature-rsa-md5 option, combines all of the 
 lines back into a single string of US-ASCII characters, converts these from base64 
 into their original (binary) form, and decrypts them using the service's public 
 key. If the result isn't the same as the message digest it computed the signature 
 is invalid. (RSAREF contains routines to do all of this work except for the 
 combining of the lines into a long string.)

All Document Modes (All Versions)

The signature-rsa-md5 label option is not supported. When this option is specified, an error that the document does not have a rating is returned.

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