Don't use C<:> as a part of a filename since many systems use that for
their own semantics (MacOS Classic for separating pathname components,
many networking schemes and utilities for separating the nodename and
-the pathname, and so on).
+the pathname, and so on). For the same reasons, avoid C<@>, C<;> and
+C<|>.
The I<portable filename characters> as defined by ANSI C are
0 1 2 3 4 5 6 7 8 9
. _ -
-and the "-" shouldn't be the first character.
+and the "-" shouldn't be the first character. If you want to be
+hypercorrect, stay within the 8.3 naming convention (all the files and
+directories have to be unique within one directory if their names are
+lowercased and truncated to eight characters before the C<.>, if any,
+and to three characters after the C<.>, if any). (And do not use
+C<.>s in directory names.)
=head2 System Interaction