L2/08-287

Public Review Issue #122

Proposal for Additional Deprecated Characters

The Unicode Technical Committee is considering giving a number of additional characters the Deprecated property.

The Deprecated property means that the use of the character is discouraged, and provides a machine-readable table for implementations. However, there are a number of characters that are marked as "discouraged" either in the text of the standard or in the names list, so the goal is to either add them to the set of characters with the Deprecated property, or if there is good reason not to, then remove the phrasing about their being discouraged. These are listed below in Table 1.

Table 2 provides additional characters that various people have proposed for Deprecation when this topic was discussed in the UTC. Table 3 gives the characters deprecated in U5.1, for comparison.

As part of this proposal, we would add text that makes the following points more clearly.

• Deprecated does not mean removed, just discouraged -- one could still get them from character encoding converters, for example.
• Whenever implementations require roundtripping to legacy encodings, deprecated characters should not be transformed or filtered -- the same as with normalization, especially NFKC.
  
• In other circumstances, deprecated characters should be avoided where possible. Where there is a preferred alternative, it should be used instead. That is generally a normalized form, but not always (see below).
  
• Certain characters cannot occur at all in text that is in normalization form NFC. This effectively discourages the use of those characters, but does not formally constitute deprecation, nor does this PRI suggest that they all be given the Deprecated property. For reference, there is a link to the list of those characters below.
  

Table 1. Discouraged

Table 2. Additional Proposed Deprecations

Table 3. U5.1 Deprecated

Table 4. Characters not occurring in NFC