Note from Mike:
contentLength is valid function when parsing. When parsing, contentLength requires us to measure how big the content region was. This is the combined length of the value region and the before padding and the after padding.

And with lengthKinds like delimited, we cannot know this number until after the parsing of the element finds the delimiter.

(This has been separated from ticket DFDL-247)

Associated requirements:
DFDL-23-127R
DFDL-23-146R
DFDL-23-142R
DFDL-23-143R
DFDL-23-144R