update commonprefix doc to make sure user is aware it works

character-by-character and that that behavior may result in it returning
prefixes that are not valid paths

diff --git a/Doc/lib/libposixpath.tex b/Doc/lib/libposixpath.tex
index 4981ac0cad906a83e450462f4905b25a6fb75596..66e278100c81a4ace70a3eae66888c6cf1470980 100644 (file)
--- a/Doc/lib/libposixpath.tex
+++ b/Doc/lib/libposixpath.tex
@@ -21,9 +21,11 @@ of the pair returned by \code{split(\var{path})}.
 \end{funcdesc}
 
 \begin{funcdesc}{commonprefix}{list}
-Return the longest string that is a prefix of all strings in
+Return the longest path prefix (taken character-by-character) that is a
+prefix of all paths in 
 \var{list}.  If \var{list} is empty, return the empty string
-(\code{''}).
+(\code{''}).  Note that this may return invalid paths because it works a
+character at a time.
 \end{funcdesc}
 
 \begin{funcdesc}{dirname}{path}