Update other_libs.md

docs/other_libs.md

@@ -25,10 +25,12 @@ See discussion after the list.
 libraries are either non-public domain, or two files, or not usable from both C and C++, or
 all three. Libraries of more than two files are mostly forbidden.
 
-For the API column, "C" means C only, "C++" means C++ only, and "C/C++C**" means C/C++ usable
-from either; even if a library includes a .cpp file it may be usable from C if the header has
-the appropriate 'extern "C"' usage, and likewise even if a library includes a .c file it may
-be usable from C++ for the same reason.
+For the API column, "C" means C only, "C++" means C++ only, and "C/C++" means C/C++ usable
+from either; some files may require *building* as C or C++ but still qualify as "C/C++" as
+long as the header file uses ~~extern "C"~~ to make it work. (In some cases, a header-file-only
+library may compile as both C or C++, but produce an implementation that can only be called from
+one or the other, because of a lack of use of ~~extern "C"~~; in this case we still qualify it
+as C/C++, as this is not an obstacle to most users.)
 
 category          | library                                                               | license              | API |files| description
 ----------------- | --------------------------------------------------------------------- |:--------------------:|:---:|:---:| -----------