Implementation-defined
=========================
* Additional non-standard character sets supported by the implementation, along with the byte alignment for each.  References: 
- Section 3, Glossary, "Character Set Encoding": "The DFDL standard allows for implementation-specific character set encodings to be supported"
- Section 11, Properties Common to both Content and Framing, encoding property
- Section 12.1.2, Mandatory Alignment for Textual Data


* Maximum specified length for binary calendar elements when dfdl:binaryCalendarRep is a packed decimal value.
Reference: Section 12.3.7.2.4 Length of Binary Calendar Elements.
See corresponding public comment and WG minutes for more details.


* Implementation-specific limitations on the use of forward and backward references in DFDL expressions.
Reference: Section 23.1 Expression Language Data Model
"Implementations may have specific limitations on the use of forward or backward reference, or may provide controls for bounding the reach of such references."
Question: Were the limitations on forward references pulled from the specification in lieu of implementation-specific limits?


Implementation-dependent
============================
* Error messages used when a processing error or schema definition error occurs while evaluating a message expression in a dfdl:assert annotation, as explained in section 7.3.1, Properties for dfdl:assert:
"If a processing error or schema definition error occurs while evaluating the message expression, a recoverable error is issued to record this error containing implementation-defined content, then processing of the assert continues as if there was no problem and in a manner consistent with the failureType property, but using an implementation-defined substitute message."

Change: "implementation-defined" in above paragraph to "implementation-dependent".


* Error messages used when a processing error or schema definition error occurs while evaluating a message expression in a dfdl:discriminator annotation, as explained in section 7.4.1, Properties for dfdl:discriminator:
"If a processing error or schema definition error occurs while evaluating the message expression, a recoverable error is issued to record this error containing implementation-defined content, then processing of the discriminator continues as if there was no problem, but in the case of failure using an implementation-defined substitute message. "

Change: "implementation-defined" in above paragraph to "implementation-dependent".