+ an unrecognized escape sequence.
+
+ ********************************************************************
+
+ #### Strategies for error annotation and coding orthogonalization
+
+ We really want to separate out a number of things. Conceptually,
+ there is a nested syntax.
+
+ At the top level is the ISO 2022 extension syntax, including charset
+ designation and invocation, and certain auxiliary controls such as the
+ ISO 6429 direction specification. These are octet-oriented, with the
+ single exception (AFAIK) of the "exit Unicode" sequence which uses the
+ UTF's natural width (1 byte for UTF-7 and UTF-8, 2 bytes for UCS-2 and
+ UTF-16, and 4 bytes for UCS-4 and UTF-32). This will be treated as a
+ (deprecated) special case in Unicode processing.
+
+ The middle layer is ISO 2022 character interpretation. This will depend
+ on the current state of the ISO 2022 registers, and assembles octets
+ into the character's internal representation.
+
+ The lowest level is translating system control conventions. At present
+ this is restricted to newline translation, but one could imagine doing
+ tab conversion or line wrapping here. "Escape from Unicode" processing
+ would be done at this level.
+
+ At each level the parser will verify the syntax. In the case of a
+ syntax error or warning (such as a redundant escape sequence that affects
+ no characters), the parser will take some action, typically inserting the
+ erroneous octets directly into the output and creating an annotation
+ which can be used by higher level I/O to mark the affected region.
+
+ This should make it possible to do something sensible about separating
+ newline convention processing from character construction, and about
+ preventing ISO 2022 escape sequences from being recognized
+ inappropriately.
+
+ The basic strategy will be to have octet classification tables, and
+ switch processing according to the table entry.
+
+ It's possible that, by doing the processing with tables of functions or
+ the like, the parser can be used for both detection and translation. */