diff --git a/punctuation.go b/punctuation.go
index 275329d..ae7ec36 100644
--- a/punctuation.go
+++ b/punctuation.go
@@ -7,8 +7,11 @@ import (
 	"strings"
 )
 
+// valid characters to extract
 const validPunc = ";:'\",!?.-()"
 
+// Extract scans the given File and returns only typical punctuation used in
+// prose.
 func Extract(f *os.File) string {
 	var out string
 	in := bufio.NewScanner(f)