+ <t hangText='d.'>The ZERO WIDTH NON-JOINER (U+200C) and ZERO WIDTH
+ JOINER (U+200D) are invisible in most contexts, but are crucial in
+ some very limited contexts. Appendix A of <xref target="RFC5892"/>
+ contains contextual restrictions for these and some other characters.
+ The use of these characters are strongly discouraged except
+ in the relevant contexts.</t>