Search from stdin no longer works / which regexp syntax? / --multiline documentation appears wrong on Manjaro package

Couple of comments from a newb.

• #795 says to use '-h' to search stdin, but that option appears to no longer be supported in ag 2.2.0-255-g7b571a8
• The '--multiline' doc says it is enabled by default, but that appears not to be the case as packaged for Manjaro 24 (or maybe for the AUR, not quite sure), at least
• The man page does not seem to specify which RE syntax is supported - presumably PCRE as it's built against that, but it would be great to be clear

This is the first RE tool that seems to make it plausible to use multiline RE search without tearing my hair out, so thanks!