Improve wording.

man/zip_file_extra_fields_count.mdoc

diff --git a/man/zip_file_extra_fields_count.mdoc b/man/zip_file_extra_fields_count.mdoc
index df60594..6dfa236 100644
--- a/man/zip_file_extra_fields_count.mdoc
+++ b/man/zip_file_extra_fields_count.mdoc
@@ -56,9 +56,9 @@
 The following flags are supported:
 .Bl -tag -width ZIP_FL_CENTRALXX -offset indent
 .It Dv ZIP_FL_CENTRAL
-Count only extra fields from the archive's central directory.
+Count extra fields from the archive's central directory.
 .It Dv ZIP_FL_LOCAL
-Count only extra fields from the local file headers.
+Count extra fields from the local file headers.
 .It Dv ZIP_FL_UNCHANGED
 Count the original unchanged extra fields, ignoring any changes made.
 .El
@@ -66,12 +66,16 @@
 The
 .Fn zip_file_extra_fields_count_by_id
 function counts the extra fields with ID (two-byte signature)
-.Ar extra_field_id
+.Ar extra_field_id .
 The other arguments are the same as for
 .Fn zip_file_extra_fields_count .
 .Pp
-Please note that the counts for local header and central directory
-extra fields do not need to sum up to the same value as when given
+Extra fields that are the same in the central directory and the local file
+header are merged into one.  Therefore, the counts with
+.Dv  ZIP_FL_CENTRAL
+and
+.Dv ZIP_FL_LOCAL
+do not need to add up to the same value as when given
 .Dv ZIP_FL_CENTRAL|ZIP_FL_LOCAL
 at once.
 .Sh RETURN VALUES