Update comment for clarity

include/git2/diff.h

@@ -88,47 +88,59 @@ typedef enum {
 	GIT_DIFF_INCLUDE_UNTRACKED = (1 << 8),
 	/** Include unmodified files in the diff list */
 	GIT_DIFF_INCLUDE_UNMODIFIED = (1 << 9),
+
 	/** Even with GIT_DIFF_INCLUDE_UNTRACKED, an entire untracked directory
 	 *  will be marked with only a single entry in the diff list; this flag
 	 *  adds all files under the directory as UNTRACKED entries, too.
 	 */
 	GIT_DIFF_RECURSE_UNTRACKED_DIRS = (1 << 10),
+
 	/** If the pathspec is set in the diff options, this flags means to
 	 *  apply it as an exact match instead of as an fnmatch pattern.
 	 */
 	GIT_DIFF_DISABLE_PATHSPEC_MATCH = (1 << 11),
+
 	/** Use case insensitive filename comparisons */
 	GIT_DIFF_DELTAS_ARE_ICASE = (1 << 12),
+
 	/** When generating patch text, include the content of untracked files */
 	GIT_DIFF_INCLUDE_UNTRACKED_CONTENT = (1 << 13),
+
 	/** Disable updating of the `binary` flag in delta records.  This is
 	 *  useful when iterating over a diff if you don't need hunk and data
 	 *  callbacks and want to avoid having to load file completely.
 	 */
 	GIT_DIFF_SKIP_BINARY_CHECK = (1 << 14),
+
 	/** Normally, a type change between files will be converted into a
 	 *  DELETED record for the old and an ADDED record for the new; this
 	 *  options enabled the generation of TYPECHANGE delta records.
 	 */
 	GIT_DIFF_INCLUDE_TYPECHANGE = (1 << 15),
+
 	/** Even with GIT_DIFF_INCLUDE_TYPECHANGE, blob->tree changes still
 	 *  generally show as a DELETED blob.  This flag tries to correctly
 	 *  label blob->tree transitions as TYPECHANGE records with new_file's
 	 *  mode set to tree.  Note: the tree SHA will not be available.
 	 */
 	GIT_DIFF_INCLUDE_TYPECHANGE_TREES  = (1 << 16),
+
 	/** Ignore file mode changes */
 	GIT_DIFF_IGNORE_FILEMODE = (1 << 17),
+
 	/** Even with GIT_DIFF_INCLUDE_IGNORED, an entire ignored directory
 	 *  will be marked with only a single entry in the diff list; this flag
 	 *  adds all files under the directory as IGNORED entries, too.
 	 */
 	GIT_DIFF_RECURSE_IGNORED_DIRS = (1 << 18),
-	/** For an untracked directory, diff can immediately label it UNTRACKED,
-	 *  but this differs from core Git which scans underneath for untracked
-	 *  or ignored files and marks the directory ignored unless it contains
-	 *  untracked files under it.  That search can be slow.  This flag makes
-	 *  diff skip ahead and immediately report the directory as untracked.
+
+	/** Core Git scans inside untracked directories, labeling them IGNORED
+	 *  if they are empty or only contain ignored files; a directory is
+	 *  consider UNTRACKED only if it has an actual untracked file in it.
+	 *  This scan is extra work for a case you often don't care about.  This
+	 *  flag makes libgit2 immediately label an untracked directory as
+	 *  UNTRACKED without looking insde it (which differs from core Git).
+	 *  Of course, ignore rules are still checked for the directory itself.
 	 */
 	GIT_DIFF_FAST_UNTRACKED_DIRS = (1 << 19),
 } git_diff_option_t;