diff --git a/unixfs/mod/dagmodifier.go b/unixfs/mod/dagmodifier.go
index 8bf9382dd..05c5c3587 100644
--- a/unixfs/mod/dagmodifier.go
+++ b/unixfs/mod/dagmodifier.go
@@ -1,3 +1,5 @@
+// Package mod provides DAG modification utilities to, for example,
+// insert additional nodes in a unixfs DAG or truncate them.
 package mod
 
 import (
@@ -19,8 +21,12 @@ import (
 	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
 )
 
-var ErrSeekFail = errors.New("failed to seek properly")
-var ErrUnrecognizedWhence = errors.New("unrecognized whence")
+// Common errors
+var (
+	ErrSeekFail           = errors.New("failed to seek properly")
+	ErrUnrecognizedWhence = errors.New("unrecognized whence")
+	ErrNotUnixfs          = fmt.Errorf("dagmodifier only supports unixfs nodes (proto or raw)")
+)
 
 // 2MB
 var writebufferSize = 1 << 21
@@ -46,8 +52,6 @@ type DagModifier struct {
 	read uio.DagReader
 }
 
-var ErrNotUnixfs = fmt.Errorf("dagmodifier only supports unixfs nodes (proto or raw)")
-
 // NewDagModifier returns a new DagModifier, the Cid prefix for newly
 // created nodes will be inherted from the passed in node.  If the Cid
 // version if not 0 raw leaves will also be enabled.  The Prefix and
@@ -412,7 +416,7 @@ func (dm *DagModifier) readPrep() error {
 	return nil
 }
 
-// Read data from this dag starting at the current offset
+// CtxReadFull reads data from this dag starting at the current offset
 func (dm *DagModifier) CtxReadFull(ctx context.Context, b []byte) (int, error) {
 	err := dm.readPrep()
 	if err != nil {
@@ -438,6 +442,8 @@ func (dm *DagModifier) HasChanges() bool {
 	return dm.wrBuf != nil
 }
 
+// Seek modifies the offset according to whence. See unixfs/io for valid whence
+// values.
 func (dm *DagModifier) Seek(offset int64, whence int) (int64, error) {
 	err := dm.Sync()
 	if err != nil {
@@ -479,6 +485,8 @@ func (dm *DagModifier) Seek(offset int64, whence int) (int64, error) {
 	return int64(dm.curWrOff), nil
 }
 
+// Truncate truncates the current Node to 'size' and replaces it with the
+// new one.
 func (dm *DagModifier) Truncate(size int64) error {
 	err := dm.Sync()
 	if err != nil {
diff --git a/unixfs/test/utils.go b/unixfs/test/utils.go
index 5e1977ddb..0ca47c842 100644
--- a/unixfs/test/utils.go
+++ b/unixfs/test/utils.go
@@ -21,6 +21,7 @@ import (
 	ipld "gx/ipfs/Qme5bWv7wtjUNGsK2BNGVUFPKiuxWrsqrtvYwCLRw8YFES/go-ipld-format"
 )
 
+// SizeSplitterGen creates a generator.
 func SizeSplitterGen(size int64) chunk.SplitterGen {
 	return func(r io.Reader) chunk.Splitter {
 		return chunk.NewSizeSplitter(r, size)
@@ -41,10 +42,13 @@ type NodeOpts struct {
 	RawLeavesUsed bool
 }
 
-var UseProtoBufLeaves = NodeOpts{Prefix: mdag.V0CidPrefix()}
-var UseRawLeaves = NodeOpts{Prefix: mdag.V0CidPrefix(), ForceRawLeaves: true, RawLeavesUsed: true}
-var UseCidV1 = NodeOpts{Prefix: mdag.V1CidPrefix(), RawLeavesUsed: true}
-var UseBlake2b256 NodeOpts
+// Some shorthands for NodeOpts.
+var (
+	UseProtoBufLeaves = NodeOpts{Prefix: mdag.V0CidPrefix()}
+	UseRawLeaves      = NodeOpts{Prefix: mdag.V0CidPrefix(), ForceRawLeaves: true, RawLeavesUsed: true}
+	UseCidV1          = NodeOpts{Prefix: mdag.V1CidPrefix(), RawLeavesUsed: true}
+	UseBlake2b256     NodeOpts
+)
 
 func init() {
 	UseBlake2b256 = UseCidV1
@@ -88,6 +92,7 @@ func GetRandomNode(t testing.TB, dserv ipld.DAGService, size int64, opts NodeOpt
 	return buf, node
 }
 
+// ArrComp checks if two byte slices are the same.
 func ArrComp(a, b []byte) error {
 	if len(a) != len(b) {
 		return fmt.Errorf("Arrays differ in length. %d != %d", len(a), len(b))