"\platform{UNIX}" should really be spelled "\platform{Unix}".
diff --git a/Doc/lib/libpopen2.tex b/Doc/lib/libpopen2.tex
index 2a87adb..6610676 100644
--- a/Doc/lib/libpopen2.tex
+++ b/Doc/lib/libpopen2.tex
@@ -2,7 +2,7 @@
          Subprocesses with accessible standard I/O streams}
 
 \declaremodule[popentwo]{standard}{popen2}
-  \platform{UNIX}
+  \platform{Unix}
 \modulesynopsis{Subprocesses with accessible standard I/O streams.}
 \sectionauthor{Drew Csillag}{drew_csillag@geocities.com}