A user has noticed that for DFDL escape schemes based on escape characters, the properties dfdl:escapeCharacter and dfdl:escapeEscapeCharacter can both be runtime-valued expressions, but not dfdl:extraEscapedCharacters.
This is not consistent. A major motivation for having these properties be runtime expressions is EDI formats, and the example motivating the need for dfdl:extraEscapedCharacters to be an expression also comes from EDIFACT.
See this Daffodil ticket with a link to the email thread discussing this: