diff --git a/pdf/core/crossrefs.go b/pdf/core/crossrefs.go
index 70f15b31..cefa1de6 100644
--- a/pdf/core/crossrefs.go
+++ b/pdf/core/crossrefs.go
@@ -25,10 +25,10 @@ const (
 	XREF_OBJECT_STREAM = iota
 )
 
-// Either can be in a normal xref table, or in an xref stream.
-// Can point either to a file offset, or to an object stream.
-// XrefFileOffset or XrefObjectStream...
-
+// XrefObject defines a cross reference entry which is a map between object number (with generation number) and the
+// location of the actual object, either as a file offset (xref table entry), or as a location within an xref
+// stream object (xref object stream).
+// TODO (v3): Unexport.
 type XrefObject struct {
 	xtype        int
 	objectNumber int
@@ -40,16 +40,26 @@ type XrefObject struct {
 	osObjIndex  int
 }
 
+// XrefTable is a map between object number and corresponding XrefObject.
+// TODO (v3): Unexport.
 type XrefTable map[int]XrefObject
 
+// ObjectStream represents an object stream's information which can contain multiple indirect objects.
+// The information specifies the number of objects and has information about offset locations for
+// each object.
+// TODO (v3): Unexport.
 type ObjectStream struct {
-	N       int
+	N       int // TODO (v3): Unexport.
 	ds      []byte
 	offsets map[int]int64
 }
 
+// ObjectStreams defines a map between object numbers (object streams only) and underlying ObjectStream information.
 type ObjectStreams map[int]ObjectStream
 
+// ObjectCache defines a map between object numbers and corresponding PdfObject. Serves as a cache for PdfObjects that
+// have already been parsed.
+// TODO (v3): Unexport.
 type ObjectCache map[int]PdfObject
 
 // Get an object from an object stream.
@@ -114,7 +124,7 @@ func (this *PdfParser) lookupObjectViaOS(sobjNumber int, objNum int) (PdfObject,
 
 		common.Log.Trace("Parsing offset map")
 		// Load the offset map (relative to the beginning of the stream...)
-		var offsets map[int]int64 = make(map[int]int64)
+		offsets := map[int]int64{}
 		// Object list and offsets.
 		for i := 0; i < int(*N); i++ {
 			this.skipSpaces()
@@ -182,11 +192,10 @@ func (this *PdfParser) lookupObjectViaOS(sobjNumber int, objNum int) (PdfObject,
 	return &io, nil
 }
 
-// Currently a bit messy.. multiple wrappers.  Can we clean up?
-
-// Outside interface for lookupByNumberWrapper.  Default attempts
-// repairs of bad xref tables.
+// LookupByNumber looks up a PdfObject by object number.  Returns an error on failure.
+// TODO (v3): Unexport.
 func (this *PdfParser) LookupByNumber(objNumber int) (PdfObject, error) {
+	// Outside interface for lookupByNumberWrapper.  Default attempts repairs of bad xref tables.
 	obj, _, err := this.lookupByNumberWrapper(objNumber, true)
 	return obj, err
 }
@@ -318,13 +327,14 @@ func (this *PdfParser) lookupByNumber(objNumber int, attemptRepairs bool) (PdfOb
 	return nil, false, errors.New("Unknown xref type")
 }
 
-// LookupByReference
+// LookupByReference looks up a PdfObject by a reference.
 func (this *PdfParser) LookupByReference(ref PdfObjectReference) (PdfObject, error) {
 	common.Log.Trace("Looking up reference %s", ref.String())
 	return this.LookupByNumber(int(ref.ObjectNumber))
 }
 
-// Trace to direct object.
+// Trace traces a PdfObject to direct object, looking up and resolving references as needed (unlike TraceToDirect).
+// TODO (v3): Unexport.
 func (this *PdfParser) Trace(obj PdfObject) (PdfObject, error) {
 	ref, isRef := obj.(*PdfObjectReference)
 	if !isRef {
diff --git a/pdf/core/stream.go b/pdf/core/stream.go
index fea5e667..fa1a8e30 100644
--- a/pdf/core/stream.go
+++ b/pdf/core/stream.go
@@ -11,7 +11,7 @@ import (
 	"github.com/unidoc/unidoc/common"
 )
 
-// Creates the encoder from the stream's dictionary.
+// NewEncoderFromStream creates a StreamEncoder based on the stream's dictionary.
 func NewEncoderFromStream(streamObj *PdfObjectStream) (StreamEncoder, error) {
 	filterObj := streamObj.PdfObjectDictionary.Get("Filter")
 	if filterObj == nil {
@@ -71,8 +71,8 @@ func NewEncoderFromStream(streamObj *PdfObjectStream) (StreamEncoder, error) {
 	}
 }
 
-// Decodes the stream.
-// Supports FlateDecode, ASCIIHexDecode, LZW.
+// DecodeStream decodes the stream data and returns the decoded data.
+// An error is returned upon failure.
 func DecodeStream(streamObj *PdfObjectStream) ([]byte, error) {
 	common.Log.Trace("Decode stream")
 
@@ -92,8 +92,7 @@ func DecodeStream(streamObj *PdfObjectStream) ([]byte, error) {
 	return decoded, nil
 }
 
-// Encodes the stream.
-// Uses the encoding specified by the object.
+// EncodeStream encodes the stream data using the encoded specified by the stream's dictionary.
 func EncodeStream(streamObj *PdfObjectStream) error {
 	common.Log.Trace("Encode stream")
 
diff --git a/pdf/core/symbols.go b/pdf/core/symbols.go
index d664eecc..e076a7a9 100644
--- a/pdf/core/symbols.go
+++ b/pdf/core/symbols.go
@@ -5,6 +5,8 @@
 
 package core
 
+// IsWhiteSpace checks if byte represents a white space character.
+// TODO (v3): Unexport.
 func IsWhiteSpace(ch byte) bool {
 	// Table 1 white-space characters (7.2.2 Character Set)
 	// spaceCharacters := string([]byte{0x00, 0x09, 0x0A, 0x0C, 0x0D, 0x20})
@@ -15,10 +17,14 @@ func IsWhiteSpace(ch byte) bool {
 	}
 }
 
+// IsFloatDigit checks if a character can be a part of a float number string.
+// TODO (v3): Unexport.
 func IsFloatDigit(c byte) bool {
 	return ('0' <= c && c <= '9') || c == '.'
 }
 
+// IsDecimalDigit checks if the character is a part of a decimal number string.
+// TODO (v3): Unexport.
 func IsDecimalDigit(c byte) bool {
 	if c >= '0' && c <= '9' {
 		return true
@@ -27,6 +33,8 @@ func IsDecimalDigit(c byte) bool {
 	}
 }
 
+// IsOctalDigit checks if a character can be part of an octal digit string.
+// TODO (v3): Unexport.
 func IsOctalDigit(c byte) bool {
 	if c >= '0' && c <= '7' {
 		return true
@@ -35,8 +43,10 @@ func IsOctalDigit(c byte) bool {
 	}
 }
 
+// IsPrintable checks if a character is printable.
 // Regular characters that are outside the range EXCLAMATION MARK(21h)
 // (!) to TILDE (7Eh) (~) should be written using the hexadecimal notation.
+// TODO (v3): Unexport.
 func IsPrintable(char byte) bool {
 	if char < 0x21 || char > 0x7E {
 		return false
@@ -44,6 +54,8 @@ func IsPrintable(char byte) bool {
 	return true
 }
 
+// IsDelimiter checks if a character represents a delimiter.
+// TODO (v3): Unexport.
 func IsDelimiter(char byte) bool {
 	if char == '(' || char == ')' {
 		return true