diff --git a/attribute/generated.go b/attribute/generated.go
index 887785b..02d05d1 100644
--- a/attribute/generated.go
+++ b/attribute/generated.go
@@ -4,6 +4,7 @@
 package attribute
 
 import "gitlab.codemonkeysoftware.net/b/hatmill"
+import "strconv"
 
 // Accept creates a "accept" attribute
 func Accept(value string) hatmill.Attrib {
@@ -146,18 +147,18 @@ func Class(value string) hatmill.Attrib {
 }
 
 // Cols creates a "cols" attribute
-func Cols(value string) hatmill.Attrib {
+func Cols(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "cols",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
 // Colspan creates a "colspan" attribute
-func Colspan(value string) hatmill.Attrib {
+func Colspan(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "colspan",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -326,10 +327,10 @@ func Headers(value string) hatmill.Attrib {
 }
 
 // Height creates a "height" attribute
-func Height(value string) hatmill.Attrib {
+func Height(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "height",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -490,11 +491,11 @@ func Max(value string) hatmill.Attrib {
 	}
 }
 
-// Maxlengh creates a "maxlengh" attribute
-func Maxlengh(value string) hatmill.Attrib {
+// Maxlength creates a "maxlength" attribute
+func Maxlength(value int) hatmill.Attrib {
 	return hatmill.Attrib{
-		Key:   "maxlengh",
-		Value: value,
+		Key:   "maxlength",
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -523,10 +524,10 @@ func Min(value string) hatmill.Attrib {
 }
 
 // Minlength creates a "minlength" attribute
-func Minlength(value string) hatmill.Attrib {
+func Minlength(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "minlength",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -652,18 +653,18 @@ func Reversed() hatmill.Attrib {
 }
 
 // Rows creates a "rows" attribute
-func Rows(value string) hatmill.Attrib {
+func Rows(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "rows",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
 // Rowspan creates a "rowspan" attribute
-func Rowspan(value string) hatmill.Attrib {
+func Rowspan(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "rowspan",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -699,10 +700,10 @@ func Shape(value string) hatmill.Attrib {
 }
 
 // Size creates a "size" attribute
-func Size(value string) hatmill.Attrib {
+func Size(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "size",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -803,10 +804,10 @@ func Summary(value string) hatmill.Attrib {
 }
 
 // Tabindex creates a "tabindex" attribute
-func Tabindex(value string) hatmill.Attrib {
+func Tabindex(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "tabindex",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
@@ -859,10 +860,10 @@ func Value(value string) hatmill.Attrib {
 }
 
 // Width creates a "width" attribute
-func Width(value string) hatmill.Attrib {
+func Width(value int) hatmill.Attrib {
 	return hatmill.Attrib{
 		Key:   "width",
-		Value: value,
+		Value: strconv.FormatInt(int64(value), 10),
 	}
 }
 
diff --git a/defs.json b/defs.json
index 6697efc..72ea458 100644
--- a/defs.json
+++ b/defs.json
@@ -18,8 +18,8 @@
     {"name": "checked", "type": "bool"},
     {"name": "cite", "type": "string"},
     {"name": "class", "type": "string"},
-    {"name": "cols", "type": "string"},
-    {"name": "colspan", "type": "string"},
+    {"name": "cols", "type": "int"},
+    {"name": "colspan", "type": "int"},
     {"name": "content", "type": "string"},
     {"name": "contenteditable", "type": "string"},
     {"name": "contextmenu", "type": "string"},
@@ -41,7 +41,7 @@
     {"name": "form", "type": "string"},
     {"name": "formaction", "type": "string"},
     {"name": "headers", "type": "string"},
-    {"name": "height", "type": "string"},
+    {"name": "height", "type": "int"},
     {"name": "hidden", "type": "bool"},
     {"name": "high", "type": "string"},
     {"name": "href", "type": "string"},
@@ -62,11 +62,11 @@
     {"name": "low", "type": "string"},
     {"name": "manifest", "type": "string"},
     {"name": "max", "type": "string"},
-    {"name": "maxlengh", "type": "string"},
+    {"name": "maxlength", "type": "int"},
     {"name": "media", "type": "string"},
     {"name": "method", "type": "string"},
     {"name": "min", "type": "string"},
-    {"name": "minlength", "type": "string"},
+    {"name": "minlength", "type": "int"},
     {"name": "multiple", "type": "bool"},
     {"name": "muted", "type": "bool"},
     {"name": "name", "type": "string"},
@@ -83,13 +83,13 @@
     {"name": "rel", "type": "string"},
     {"name": "required", "type": "bool"},
     {"name": "reversed", "type": "bool"},
-    {"name": "rows", "type": "string"},
-    {"name": "rowspan", "type": "string"},
+    {"name": "rows", "type": "int"},
+    {"name": "rowspan", "type": "int"},
     {"name": "sandbox", "type": "string"},
     {"name": "scope", "type": "string"},
     {"name": "selected", "type": "bool"},
     {"name": "shape", "type": "string"},
-    {"name": "size", "type": "string"},
+    {"name": "size", "type": "int"},
     {"name": "sizes", "type": "string"},
     {"name": "slot", "type": "string"},
     {"name": "span", "type": "string"},
@@ -102,14 +102,14 @@
     {"name": "step", "type": "string"},
     {"name": "style", "type": "string"},
     {"name": "summary", "type": "string"},
-    {"name": "tabindex", "type": "string"},
+    {"name": "tabindex", "type": "int"},
     {"name": "target", "type": "string"},
     {"name": "title", "type": "string"},
     {"name": "translate", "type": "string"},
     {"name": "type", "type": "string"},
     {"name": "usemap", "type": "string"},
     {"name": "value", "type": "string"},
-    {"name": "width", "type": "string"},
+    {"name": "width", "type": "int"},
     {"name": "wrap", "type": "string"}
   ],
   "elements": [
diff --git a/hatmill_test.go b/hatmill_test.go
index f18e605..a9bd1df 100644
--- a/hatmill_test.go
+++ b/hatmill_test.go
@@ -190,9 +190,10 @@ func Example() {
 				he.Img(ha.Src("./me.jpg"), ha.Id("profile-photo")),
 				hatmill.Text(html.EscapeString(userInput)),
 				he.Div(ha.Disabled(), ha.CustomData("coolness", "awesome"))(),
+				he.Textarea(ha.Height(25))(),
 			),
 		),
 	)
 	hatmill.WriteDocument(os.Stdout, document)
-	// Output: <!DOCTYPE html><html><head><meta http-equiv='refresh' content='5'></head><body><div><img src='./me.jpg' id='profile-photo'>&lt;script&gt;launchMissiles();&lt;/script&gt;<div disabled data-coolness='awesome'></div></div></body></html>
+	// Output: <!DOCTYPE html><html><head><meta http-equiv='refresh' content='5'></head><body><div><img src='./me.jpg' id='profile-photo'>&lt;script&gt;launchMissiles();&lt;/script&gt;<div disabled data-coolness='awesome'></div><textarea height='25'></textarea></div></body></html>
 }
diff --git a/internal/codegen/codegen.go b/internal/codegen/codegen.go
index 2c9aecc..f437b4f 100644
--- a/internal/codegen/codegen.go
+++ b/internal/codegen/codegen.go
@@ -19,59 +19,67 @@ func identifier(s string) string {
 	return strings.Join(words, "")
 }
 
-var attribTypes = map[string]string {
-	"string":  `// %[1]s creates a "%[2]s" attribute
-	func %[1]s(value string) hatmill.Attrib {
-		return hatmill.Attrib{
-			Key: "%[2]s",
-			Value: value,
-		}
-	}
-	`,
+type AttribTypeInfo struct {
+	Template string
+	Imports  []string
+}
 
-	"bool": `// %[1]s creates a "%[2]s" attribute
-	func %[1]s() hatmill.Attrib {
-		return hatmill.Attrib{
-			Key: "%[2]s",
+var attribTypes = map[string]AttribTypeInfo{
+	"string": {
+		Template: `// %[1]s creates a "%[2]s" attribute
+		func %[1]s(value string) hatmill.Attrib {
+			return hatmill.Attrib{
+				Key: "%[2]s",
+				Value: value,
+			}
 		}
-	}
-	`,
+		`,
+	},
+
+	"bool": {
+		Template: `// %[1]s creates a "%[2]s" attribute
+		func %[1]s() hatmill.Attrib {
+			return hatmill.Attrib{
+				Key: "%[2]s",
+			}
+		}
+		`,
+	},
+
+	"int": {
+		Template: `// %[1]s creates a "%[2]s" attribute
+		func %[1]s(value int) hatmill.Attrib {
+			return hatmill.Attrib{
+				Key: "%[2]s",
+				Value: strconv.FormatInt(int64(value), 10),
+			}
+		}
+		`,
+		Imports: []string{"strconv"},
+	},
+}
+
+// Def represents a top-level definition and its required imports.
+type Def struct {
+	Source  string
+	Imports []string
+}
+
+type Spec interface {
+	Generate() Def
 }
 
 type AttribSpec struct {
-	Name string     `json:"name"`
+	Name string `json:"name"`
 	Type string `json:"type"`
 }
 
-type AttribSpecs []AttribSpec
-
-func (a AttribSpecs) Code() Code {
-	var c Code
-	const hatmillImport = "gitlab.codemonkeysoftware.net/b/hatmill"
-
-	c.Imports = append(c.Imports, hatmillImport)
-	for _, spec := range a {
-		c.Defs = append(c.Defs, spec.Generate())
+func (spec AttribSpec) Generate() Def {
+	template := attribTypes[spec.Type].Template
+	return Def{
+		Source:  fmt.Sprintf(template, identifier(spec.Name), spec.Name),
+		Imports: attribTypes[spec.Type].Imports,
 	}
-	return c
-}
-
-type ElemSpecs []ElemSpec
-
-func (e ElemSpecs) Code() Code {
-	var c Code
-	const hatmillImport = "gitlab.codemonkeysoftware.net/b/hatmill"
-
-	c.Imports = append(c.Imports, hatmillImport)
-	for _, spec := range e {
-		c.Defs = append(c.Defs, spec.Generate())
-	}
-	return c
-}
-
-func (def AttribSpec) Generate() string {
-	template := attribTypes[def.Type]
-	return fmt.Sprintf(template, identifier(def.Name), def.Name)
 }
 
 type ElemSpec struct {
@@ -79,7 +87,7 @@ type ElemSpec struct {
 	Void bool   `json:"void"`
 }
 
-func (def ElemSpec) Generate() string {
+func (spec ElemSpec) Generate() Def {
 	const (
 		parentTemplate = `// %[1]s creates a <%[2]s> element.
         func %[1]s(attribs ...hatmill.Attrib) func(children ...hatmill.Term) hatmill.ParentElement {
@@ -105,48 +113,52 @@ func (def ElemSpec) Generate() string {
 	)
 
 	template := parentTemplate
-	if def.Void {
+	if spec.Void {
 		template = voidTemplate
 	}
-	return fmt.Sprintf(template, identifier(def.Name), def.Name)
+	return Def{
+		Source: fmt.Sprintf(template, identifier(spec.Name), spec.Name),
+	}
 }
 
-type Specs struct {
-	Attributes AttribSpecs `json:"attributes"`
-	Elements   ElemSpecs   `json:"elements"`
-}
-
-// Code is a very slight abstraction of a source code file.
-type Code struct {
-	Package string
-	Imports []string
-	Defs []string
-}
-
-func (c Code) Bytes() ([]byte, error) {
+func Render(defs []Def, pkgName string) ([]byte, error) {
 	buf := new(bytes.Buffer)
 	buf.WriteString(`// GENERATED BY gitlab.codemonkeysoftware.net/b/hatmill/internal/codegen
 	// DO NOT EDIT!
 
 	`)
-	fmt.Fprintln(buf, "package ", c.Package)
-	for _, imp := range c.Imports {
+	fmt.Fprintln(buf, "package ", pkgName)
+	buf.WriteString(`import "gitlab.codemonkeysoftware.net/b/hatmill"
+	`)
+
+	// Print each import only once.
+	imports := make(map[string]struct{})
+	for _, def := range defs {
+		for _, imp := range def.Imports {
+			imports[imp] = struct{}{}
+		}
+	}
+	for imp := range imports {
 		fmt.Fprintf(buf, "import \"%s\"\n", imp)
 	}
-	for _, def := range c.Defs {
-		buf.WriteString(def)
+
+	for _, def := range defs {
+		buf.WriteString(def.Source)
 	}
-	return format.Source(buf.Bytes())
+
+	formatted, err := format.Source(buf.Bytes())
+	if err != nil {
+		err = fmt.Errorf("generated invalid code: %s\nSource code:\n%s", err, buf)
+	}
+	return formatted, err
 }
 
-type Coder interface {
-	Code() Code
-}
-
-func WriteCodeFile(c Coder, path, pkg string) error {
-	code := c.Code()
-	code.Package = pkg
-	b, err := code.Bytes()
+func WriteCodeFile(specs []Spec, path, pkgName string) error {
+	var defs []Def
+	for _, spec := range specs {
+		defs = append(defs, spec.Generate())
+	}
+	b, err := Render(defs, pkgName)
 	if err != nil {
 		return err
 	}
@@ -166,19 +178,32 @@ func main() {
 		log.Fatal(err)
 	}
 
-	var specs Specs
+	var specs struct {
+		AttribSpecs []AttribSpec `json:"attributes"`
+		ElemSpecs   []ElemSpec   `json:"elements"`
+	}
+
 	err = json.Unmarshal(input, &specs)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	err = WriteCodeFile(specs.Attributes, *attribPath, *attribPkg)
+	var attribSpecs []Spec
+	for _, spec := range specs.AttribSpecs {
+		attribSpecs = append(attribSpecs, spec)
+	}
+	err = WriteCodeFile(attribSpecs, *attribPath, *attribPkg)
 	if err != nil {
 		log.Fatal(err)
 	}
 
-	err = WriteCodeFile(specs.Elements, *elemPath, *elemPkg)
+	var elemSpecs []Spec
+	for _, spec := range specs.ElemSpecs {
+		elemSpecs = append(elemSpecs, spec)
+	}
+	err = WriteCodeFile(elemSpecs, *elemPath, *elemPkg)
 	if err != nil {
 		log.Fatal(err)
 	}
+
 }