diff --git a/HTMLKit/HTMLDocumentType.m b/HTMLKit/HTMLDocumentType.m
index e6d890b..e63fd16 100644
--- a/HTMLKit/HTMLDocumentType.m
+++ b/HTMLKit/HTMLDocumentType.m
@@ -7,6 +7,7 @@
 //
 
 #import "HTMLDocumentType.h"
+#import "NSString+HTMLKit.h"
 
 NS_INLINE BOOL nilOrEqual(id first, id second) {
 	return (first == nil) || ([first isEqual:second]);
@@ -86,13 +87,13 @@ NS_INLINE BOOL nilOrEqual(id first, id second) {
 		return HTMLQuirksModeQuirks;
 	}
 
-	if (isEqualCaseInsensitive(_publicIdentifier, @"-//W3O//DTD W3 HTML Strict 3.0//EN//") ||
-		isEqualCaseInsensitive(_publicIdentifier, @"-/W3C/DTD HTML 4.0 Transitional/EN") ||
-		isEqualCaseInsensitive(_publicIdentifier, @"HTML")) {
+	if ([_publicIdentifier isEqualToStringIgnoringCase:@"-//W3O//DTD W3 HTML Strict 3.0//EN//"] ||
+		[_publicIdentifier isEqualToStringIgnoringCase:@"-/W3C/DTD HTML 4.0 Transitional/EN"] ||
+		[_publicIdentifier isEqualToStringIgnoringCase:@"HTML"]) {
 		return HTMLQuirksModeQuirks;
 	}
 	
-	if (isEqualCaseInsensitive(_systemIdentifier, @"http://www.ibm.com/data/dtd/v11/ibmxhtml1-transitional.dtd")) {
+	if ([_publicIdentifier isEqualToStringIgnoringCase:@"http://www.ibm.com/data/dtd/v11/ibmxhtml1-transitional.dtd"]) {
 		return HTMLQuirksModeQuirks;
 	}
 
@@ -101,21 +102,21 @@ NS_INLINE BOOL nilOrEqual(id first, id second) {
 	}
 
 	if (_systemIdentifier == nil) {
-		if (hasPrefixCaseInsensitive(_publicIdentifier, @"-//W3C//DTD HTML 4.01 Frameset//") ||
-			hasPrefixCaseInsensitive(_publicIdentifier, @"-//W3C//DTD HTML 4.01 Transitional//")) {
+		if ([_publicIdentifier hasPrefixIgnoringCase:@"-//W3C//DTD HTML 4.01 Frameset//"] ||
+			[_publicIdentifier hasPrefixIgnoringCase:@"-//W3C//DTD HTML 4.01 Transitional//"]) {
 			return HTMLQuirksModeQuirks;
 		}
 	}
 
 #warning Check "iframe srcdoc"
-	if (hasPrefixCaseInsensitive(_publicIdentifier, @"-//W3C//DTD XHTML 1.0 Frameset//") ||
-		hasPrefixCaseInsensitive(_publicIdentifier, @"-//W3C//DTD XHTML 1.0 Transitional//")) {
+	if ([_publicIdentifier hasPrefixIgnoringCase:@"-//W3C//DTD XHTML 1.0 Frameset//"] ||
+		[_publicIdentifier hasPrefixIgnoringCase:@"-//W3C//DTD XHTML 1.0 Transitional//"]) {
 		return HTMLQuirksModeLimitedQuirks;
 	}
 
 	if (_systemIdentifier != nil) {
-		if (hasPrefixCaseInsensitive(_publicIdentifier, @"-//W3C//DTD HTML 4.01 Frameset//") ||
-			hasPrefixCaseInsensitive(_publicIdentifier, @"-//W3C//DTD HTML 4.01 Transitional//")) {
+		if ([_publicIdentifier hasPrefixIgnoringCase:@"-//W3C//DTD HTML 4.01 Frameset//"] ||
+			[_publicIdentifier hasPrefixIgnoringCase:@"-//W3C//DTD HTML 4.01 Transitional//"]) {
 			return HTMLQuirksModeLimitedQuirks;
 		}
 	}
diff --git a/HTMLKit/HTMLQuirksMode.h b/HTMLKit/HTMLQuirksMode.h
index e5caf19..3ad4920 100644
--- a/HTMLKit/HTMLQuirksMode.h
+++ b/HTMLKit/HTMLQuirksMode.h
@@ -6,6 +6,8 @@
 //  Copyright (c) 2015 BrainCookie. All rights reserved.
 //
 
+#import "NSString+HTMLKit.h"
+
 typedef NS_ENUM(short, HTMLQuirksMode)
 {
 	HTMLQuirksModeNoQuirks,
@@ -76,20 +78,10 @@ static NSString * HTMLQuirksModePrefixes[] = {
 #undef QUIRKS_ENTRY
 };
 
-NS_INLINE BOOL isEqualCaseInsensitive(NSString *first, NSString *second) {
-	return [first caseInsensitiveCompare:second] == NSOrderedSame;
-}
-
-NS_INLINE BOOL hasPrefixCaseInsensitive(NSString *string, NSString *prefix) {
-	NSRange reange = [string rangeOfString:prefix
-								   options:NSAnchoredSearch|NSCaseInsensitiveSearch];
-	return reange.location != NSNotFound;
-}
-
 NS_INLINE BOOL QuirksModePrefixMatch(NSString *publicIdentifier)
 {
 	for (int i = 0; i < sizeof(HTMLQuirksModePrefixes) / sizeof(HTMLQuirksModePrefixes[0]); i++) {
-		if (hasPrefixCaseInsensitive(publicIdentifier, HTMLQuirksModePrefixes[i])) {
+		if ([publicIdentifier hasPrefixIgnoringCase:HTMLQuirksModePrefixes[i]]) {
 			return YES;
 		}
 	}
diff --git a/HTMLKit/NSString+HTMLKit.h b/HTMLKit/NSString+HTMLKit.h
index 146c89e..5f2e9fd 100644
--- a/HTMLKit/NSString+HTMLKit.h
+++ b/HTMLKit/NSString+HTMLKit.h
@@ -10,7 +10,9 @@
 
 @interface NSString (HTMLKit)
 
+- (BOOL)isEqualToStringIgnoringCase:(NSString *)aString;
 - (BOOL)isEqualToAny:(NSString *)first, ... NS_REQUIRES_NIL_TERMINATION;
+- (BOOL)hasPrefixIgnoringCase:(NSString *)aString;
 - (BOOL)isHTMLWhitespaceString;
 - (BOOL)containsHTMLWhitespace;
 - (NSUInteger)leadingWhitespaceLength;
diff --git a/HTMLKit/NSString+HTMLKit.m b/HTMLKit/NSString+HTMLKit.m
index 114ffa2..fe4d8b7 100644
--- a/HTMLKit/NSString+HTMLKit.m
+++ b/HTMLKit/NSString+HTMLKit.m
@@ -15,6 +15,11 @@ NS_INLINE BOOL isHtmlWhitespaceChar(char c)
 
 @implementation NSString (HTMLKit)
 
+- (BOOL)isEqualToStringIgnoringCase:(NSString *)aString
+{
+	return [self caseInsensitiveCompare:aString] == NSOrderedSame;
+}
+
 - (BOOL)isEqualToAny:(NSString *)first, ... NS_REQUIRES_NIL_TERMINATION
 {
 	va_list list;
@@ -28,6 +33,13 @@ NS_INLINE BOOL isHtmlWhitespaceChar(char c)
 	return NO;
 }
 
+- (BOOL)hasPrefixIgnoringCase:(NSString *)aString
+{
+	NSRange reange = [self rangeOfString:aString
+								 options:NSAnchoredSearch|NSCaseInsensitiveSearch];
+	return reange.location != NSNotFound;
+}
+
 - (BOOL)isHTMLWhitespaceString
 {
 	NSCharacterSet *set = [[NSCharacterSet characterSetWithCharactersInString:@" \t\n\f\r"] invertedSet];