clarification needed in RegEx guide

[ctcpip]

in https://github.com/ossf/wg-best-practices-os-developers/blob/main/docs/Correctly-Using-Regular-Expressions.md, the following text appears in the Java row: “\z”; “$” works but some documents conflict

What does this mean exactly? Let's add some information/context to this in the guide. Alternately, remove the qualification ("but...") if it's not needed. My understanding is that Java $ will only match the end of the input (when not in multiline mode; equivalent to \z) and is therefore safe to use.

cc @david-a-wheeler

[david-a-wheeler]

The "Rationale" goes into detail. Some Oracle documentation directly conflicts with what actually happens.