-gnatyD was documented in the user guide but not in `gnat --help-ada`.
gcc/ada/
* usage.adb (Usage): Document -gnatyD.
Write_Line (" c check comment format (two spaces)");
Write_Line (" C check comment format (one space)");
Write_Line (" d check no DOS line terminators");
+ Write_Line (" D check declared identifiers in mixed case");
Write_Line (" e check end/exit labels present");
Write_Line (" f check no form feeds/vertical tabs in source");
Write_Line (" g check standard GNAT style rules, same as ydISux");