diff --git a/tools/exp/main.go b/tools/exp/main.go
index 8a65c84..9d77af8 100644
--- a/tools/exp/main.go
+++ b/tools/exp/main.go
@@ -9,6 +9,7 @@ import (
 	"github.com/cjslep/activity/tools/exp/rdf"
 	"github.com/cjslep/activity/tools/exp/rdf/owl"
 	"github.com/cjslep/activity/tools/exp/rdf/rdfs"
+	"github.com/cjslep/activity/tools/exp/rdf/rfc"
 	"github.com/cjslep/activity/tools/exp/rdf/schema"
 	"github.com/cjslep/activity/tools/exp/rdf/xsd"
 	"io/ioutil"
@@ -33,6 +34,7 @@ func init() {
 	mustAddOntology(&rdf.RDFOntology{Package: "rdf"})
 	mustAddOntology(&rdfs.RDFSchemaOntology{})
 	mustAddOntology(&schema.SchemaOntology{})
+	mustAddOntology(&rfc.RFCOntology{Package: "rfc"})
 }
 
 var (
diff --git a/tools/exp/rdf/rfc/ontology.go b/tools/exp/rdf/rfc/ontology.go
new file mode 100644
index 0000000..e4aed1c
--- /dev/null
+++ b/tools/exp/rdf/rfc/ontology.go
@@ -0,0 +1,148 @@
+// Package RFC contains ontology values that are defined in RFCs, BCPs, and
+// other miscellaneous standards.
+package rfc
+
+import (
+	"fmt"
+	"github.com/cjslep/activity/tools/exp/codegen"
+	"github.com/cjslep/activity/tools/exp/rdf"
+	"github.com/dave/jennifer/jen"
+	"net/url"
+	"strings"
+)
+
+const (
+	rfcSpec   = "https://tools.ietf.org/html/"
+	bcp47Spec = "bcp47"
+)
+
+type RFCOntology struct {
+	Package string
+}
+
+func (o *RFCOntology) SpecURI() string {
+	return rfcSpec
+}
+
+func (o *RFCOntology) Load() ([]rdf.RDFNode, error) {
+	return o.LoadAsAlias("")
+}
+
+func (o *RFCOntology) LoadAsAlias(s string) ([]rdf.RDFNode, error) {
+	return []rdf.RDFNode{
+		&rdf.AliasedDelegate{
+			Spec:     rfcSpec,
+			Alias:    s,
+			Name:     bcp47Spec,
+			Delegate: &bcp47{pkg: o.Package},
+		},
+	}, nil
+}
+
+func (o *RFCOntology) LoadSpecificAsAlias(alias, name string) ([]rdf.RDFNode, error) {
+	switch name {
+	case bcp47Spec:
+		return []rdf.RDFNode{
+			&rdf.AliasedDelegate{
+				Spec:     "",
+				Alias:    "",
+				Name:     alias,
+				Delegate: &bcp47{pkg: o.Package},
+			},
+		}, nil
+	}
+	return nil, fmt.Errorf("rfc ontology cannot find %q to alias to %q", name, alias)
+}
+
+func (o *RFCOntology) LoadElement(name string, payload map[string]interface{}) ([]rdf.RDFNode, error) {
+	return nil, nil
+}
+
+func (o *RFCOntology) GetByName(name string) (rdf.RDFNode, error) {
+	name = strings.TrimPrefix(name, o.SpecURI())
+	switch name {
+	case bcp47Spec:
+		return &bcp47{pkg: o.Package}, nil
+	}
+	return nil, fmt.Errorf("rfc ontology could not find node for name %s", name)
+}
+
+var _ rdf.RDFNode = &bcp47{}
+
+type bcp47 struct {
+	pkg string
+}
+
+func (b *bcp47) Enter(key string, ctx *rdf.ParsingContext) (bool, error) {
+	return true, fmt.Errorf("bcp47 langaugetag cannot be entered")
+}
+
+func (b *bcp47) Exit(key string, ctx *rdf.ParsingContext) (bool, error) {
+	return true, fmt.Errorf("bcp47 languagetag cannot be exited")
+}
+
+func (b *bcp47) Apply(key string, value interface{}, ctx *rdf.ParsingContext) (bool, error) {
+	v := ctx.Result.GetReference(rfcSpec)
+	if len(v.Values[bcp47Spec].Name) == 0 {
+		u, err := url.Parse(rfcSpec + bcp47Spec)
+		if err != nil {
+			return true, err
+		}
+		val := &rdf.VocabularyValue{
+			Name:           bcp47Spec,
+			URI:            u,
+			DefinitionType: jen.String(),
+			Zero:           "\"\"",
+			IsNilable:      false,
+			SerializeFn: rdf.SerializeValueFunction(
+				b.pkg,
+				bcp47Spec,
+				jen.String(),
+				[]jen.Code{
+					jen.Return(
+						jen.Id(codegen.This()),
+						jen.Nil(),
+					),
+				}),
+			DeserializeFn: rdf.DeserializeValueFunction(
+				b.pkg,
+				bcp47Spec,
+				jen.String(),
+				[]jen.Code{
+					jen.If(
+						jen.List(
+							jen.Id("s"),
+							jen.Id("ok"),
+						).Op(":=").Id(codegen.This()).Assert(jen.String()),
+						jen.Id("ok"),
+					).Block(
+						jen.Return(
+							jen.Id("s"),
+							jen.Nil(),
+						),
+					).Else().Block(
+						jen.Return(
+							jen.Lit(""),
+							jen.Qual("fmt", "Errorf").Call(
+								jen.Lit("%v cannot be interpreted as a string for bcp47 languagetag"),
+								jen.Id(codegen.This()),
+							),
+						),
+					),
+				}),
+			LessFn: rdf.LessFunction(
+				b.pkg,
+				bcp47Spec,
+				jen.String(),
+				[]jen.Code{
+					jen.Return(
+						jen.Id("lhs").Op("<").Id("rhs"),
+					),
+				}),
+		}
+		if err = v.SetValue(bcp47Spec, val); err != nil {
+			return true, err
+		}
+	}
+	return true, nil
+}
diff --git a/tools/exp/spec.json b/tools/exp/spec.json
index d4e2d5f..ea6439d 100644
--- a/tools/exp/spec.json
+++ b/tools/exp/spec.json
@@ -4,6 +4,7 @@
       "owl": "http://www.w3.org/2002/07/owl#",
       "rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns#",
       "rdfs": "http://www.w3.org/2000/01/rdf-schema#",
+      "rfc": "https://tools.ietf.org/html/",
       "schema": "http://schema.org/",
       "xsd": "http://www.w3.org/2001/XMLSchema#"
     },
@@ -4021,7 +4022,7 @@
           "isDefinedBy": "https://www.w3.org/TR/activitystreams-vocabulary/#dfn-hreflang",
           "range": {
             "type": "owl:Class",
-            "unionOf": []
+            "unionOf": "rfc:bcp47"
           },
           "name": "hreflang",
           "url": "https://www.w3.org/TR/activitystreams-vocabulary/#dfn-hreflang"