+=func is_readable
+
+=func is_writable
+
+ $bool = is_readable($mode);
+ $bool = is_writable($mode);
+
+Determine of an C<fopen>-style mode is readable, writable or both.
+
+=cut
+
+sub is_readable { $_[0] !~ /^[aw]b?$/ }
+sub is_writable { $_[0] !~ /^rb?$/ }
+