I am in the process of installing SDL 2 on Mac OSX 10.9 via macports, and for reference I have been following the official documentation as well as any sdl-specific information I can find.
https://guide.macports.org/ is straight-forward, as is:
https://guide.macports.org/#using.variants.invoking
I see that sdl2lib is available...
libsdl2 has the variants:
universal: Build for multiple architectures
x11: Enable X11 support
but despite having looked through pages at the above links and having searched for documentation for "SDL with X11", I can't seem to find information about whether I need X11 (and/or universal AKA powerpc) support. I wouldn't want to install SDL only to find that something is broken or missing. Then again, there were some issues with X11 being enabled by default back when Mac OSX 10.1 was new: https://forums.libsdl.org/viewtopic.php?t=2871&sid=52ca72a72c285196dd25fd8619715ae9
(That is another problem: much of the information I discover applies to outdated operating systems.)
Apparently SDL wasn't thread-safe at one point unless you used X11, but this was mentioned when SDL verson 1 was the main version: http://forum.freegamedev.net/viewtopic.php?f=3&t=1078
How am I meant to proceed (Which flags, if any, are usually chosen?)
port install libsdl2 <???>
I would appreciate any help and follow-up warnings for the next stepsinstallation steps. Thank you in advance.
Most people have moved to Homebrew as their package system, but Macports should work just fine.
Universal does not mean PowerPC necessarily. In fact almost no one needs it anymore. Universal means a fat binary, which architectures this defines is set in your Macports configuration.
SDL2 should work just fine under Quartz, no need to have X11 - as also makes deployment annoying and difficult as you need to have XQuartz installed.
Also don't be afraid to reinstall SDL2 with other options if you miss something, it shouldn't take to long.
TL;DR Just install it without any additional flags unless you discover you need something special.