+@float NOTE
+When using AviSynth+'s installed headers, the user must also pass
+the avisynth/ include directory to @code{--extra-cflags}. For example,
+if the PREFIX given to AviSynth+'s Makefile was /usr/i686-w64-mingw32,
+then the correct command would be
+@code{--extra-cflags="-I/usr/i686-w64-mingw32/include/avisynth"}.
+@end float
+
+For Linux and OS X, the supported AviSynth variant is
+@url{https://github.com/avxsynth/avxsynth, AvxSynth}.
+@file{avxsynth_c.h} is installed as part of the normal
+build routine, as illustrated on
+@url{https://github.com/avxsynth/avxsynth/wiki/System-Setup, AvxSynth's wiki}.
+(the instructions for compiling its prerequisites are outdated, as FFMS 2.18
+or higher is now needed; the list of dependencies to be downloaded from the
+repositories is still the same, though).
+
+@float NOTE
+AviSynth and AvxSynth are loaded dynamically. Distributors can build Libav
+with @code{--enable-avisynth}, and the binaries will work regardless of the
+end user having AviSynth or AvxSynth installed - they'll only need to be
+installed to use AviSynth scripts (obviously).
+@end float