Documented the runtimemodel attribute.
diff --git a/Doc/mac/libmacos.tex b/Doc/mac/libmacos.tex
index 60e7f9b..5a2caf2 100644
--- a/Doc/mac/libmacos.tex
+++ b/Doc/mac/libmacos.tex
@@ -12,6 +12,12 @@
Note the capitalisation of the module name, this is a historical
artifact.
+\begin{datadesc}{runtimemodel}
+Either \code{"ppc"}, \code{"carbon"} or \code{"macho"}. This signifies
+whether this Python uses the classic (InterfaceLib style) runtime
+model, the MacOS X compatible CarbonLib style or the MacOS X-only
+Mach-O style.
+\end{datadesc}
\begin{excdesc}{Error}
This exception is raised on MacOS generated errors, either from