diff --git a/colors.go b/colors.go
index eca0f23..9a9e914 100644
--- a/colors.go
+++ b/colors.go
@@ -8,6 +8,8 @@ import (
 
 type terminalColor uint32
 
+// Theme is used to associate color names to integer color values ;
+// the color names in the theme are available in the colorizing format
 type Theme map[string]terminalColor
 
 var theme Theme = make(map[string]terminalColor)
diff --git a/printer.go b/printer.go
index 95f25c4..bb83fa2 100644
--- a/printer.go
+++ b/printer.go
@@ -30,8 +30,8 @@ func Sprintf(format string, a ...interface{}) (string, error) {
 		cursor = match[1]
 
 		// (2) extract features
+		var err error
 		var (
-			err         = error(nil)
 			text        = ""
 			sForeground = ""
 			sBackground = ""
@@ -76,6 +76,7 @@ func Sprintf(format string, a ...interface{}) (string, error) {
 	return output, nil
 }
 
+// Printf prints a terminal-colorized output following the coloring format
 func Printf(format string, a ...interface{}) error {
 	s, err := Sprintf(format, a...)
 	if err != nil {