Update GUIDE.md

GUIDE.md

@@ -458,9 +458,24 @@ destination storage and is required.
 
 An include pattern starts with +, and an exclude pattern starts with -.  Patterns may contain wildcard characters * which matches a path string of any length, and ? matches a single character.  Note that both * and ? will match any character including the path separator /.
 
+The path separator is always /, even on Windows.
+
 When matching a path against a list of patterns, the path is compared with the part after + or -, one pattern at a time.  Therefore, the order of the patterns is significant.  If a match with an include pattern is found, the path is said to be included without further comparisons.  If a match with an exclude pattern is found, the path is said to be excluded without further comparison.  If a match is not found, the path will be excluded if all patterns are include patterns, but included otherwise.
 
-Patterns ending with a / apply to directories only, and patterns not ending with a / apply to files only.  When a directory is excluded, all files and subdirectires under it will also be excluded.  Note that the path separator is always /, even on Windows.
+Patterns ending with a / apply to directories only, and patterns not ending with a / apply to files only.  Patterns ending with * and ?, however, apply to both directories and files.  When a directory is excluded, all files and subdirectories under it will also be excluded.  Therefore, to include a subdirectory, all parent directories must be explicitly included.  For instance, the following pattern list doesn't do what is intended, since the `foo` directory will be excluded so the `foo/bar` will never be visited:
+
+```
++foo/bar/*
+-*
+```
+
+The correct way is to include `foo` as well:
+
+```
++foo/bar/*
++foo/
+-*
+```
 
 The following pattern list includes only files under the directory foo/ but not files under the subdirectory foo/bar: