Source: Interlinear annotation ad hoc group
Date: December 4, 1998
The following text is an improved set of notes concerning the PDAM 30 interlinear annotation characters. These notes will be used to produce a US comment including a proposed Annex P entries for these 3 characters (whole or summarized).
These new characters are used in internal processing when out of band information is associated with a character stream, very similarly to the usage of the U+FFFC OBJECT REPLACEMENT CHARACTER. However unlike objects hidden by the latter character, the annotation itself is textual.
The usage of these new characters in plain text interchange is strongly discouraged without prior agreement between the sender and the receiver, because otherwise the content may be misinterpreted. Simply filtering out these new characters on input will produce an unreadable result, or even worse, an opposite meaning.
On input a plain text receiver should either preserve all characters, or remove the interlinear annotation characters as well as the annotation text included between the interlinear annotation separator and the interlinear annotation terminator.
When an output for plain text usage is desired and when the receiver is unknown to the sender, these interlinear annotation characters should be removed as well as the annotation text included between the interlinear annotation separator and the interlinear annotation terminator.
This doesn’t preclude their usage in plain text interchange, but it requires a prior agreement between the sender and the receiver as for the interpretation of the annotations.