OK it seems they changed the doc since. In the docs for JDK 21 we read instead [1]:

> If MULTILINE mode is not activated, the regular expression ^ ignores line terminators and only matches at the beginning of the entire input sequence. The regular expression $ matches at the end of the entire input sequence, but also matches just before the last line terminator if this is not followed by any other input character. Other line terminators are ignored, including the last one if it is followed by other input characters.

Looks like I have some code to fix.

[1] https://docs.oracle.com/en%2Fjava%2Fjavase%2F21%2Fdocs%2Fapi...