diff --git a/core/fxcrt/bytestring.cpp b/core/fxcrt/bytestring.cpp
index 8b07981..a353064 100644
--- a/core/fxcrt/bytestring.cpp
+++ b/core/fxcrt/bytestring.cpp
@@ -469,7 +469,7 @@
   return m_pData ? m_pData->m_nRefs : 0;
 }
 
-ByteString ByteString::Mid(size_t first, size_t count) const {
+ByteString ByteString::Substr(size_t first, size_t count) const {
   if (!m_pData)
     return ByteString();
 
@@ -493,13 +493,13 @@
 ByteString ByteString::Left(size_t count) const {
   if (count == 0 || !IsValidLength(count))
     return ByteString();
-  return Mid(0, count);
+  return Substr(0, count);
 }
 
 ByteString ByteString::Right(size_t count) const {
   if (count == 0 || !IsValidLength(count))
     return ByteString();
-  return Mid(GetLength() - count, count);
+  return Substr(GetLength() - count, count);
 }
 
 void ByteString::AllocCopy(ByteString& dest,
diff --git a/core/fxcrt/bytestring.h b/core/fxcrt/bytestring.h
index 11c372b..c7d09aa 100644
--- a/core/fxcrt/bytestring.h
+++ b/core/fxcrt/bytestring.h
@@ -163,7 +163,7 @@
   pdfium::span<char> GetBuffer(size_t nMinBufLength);
   void ReleaseBuffer(size_t nNewLength);
 
-  ByteString Mid(size_t first, size_t count) const;
+  ByteString Substr(size_t first, size_t count) const;
   ByteString Left(size_t count) const;
   ByteString Right(size_t count) const;
 
diff --git a/core/fxcrt/bytestring_unittest.cpp b/core/fxcrt/bytestring_unittest.cpp
index d0eab1a..61b4ae1 100644
--- a/core/fxcrt/bytestring_unittest.cpp
+++ b/core/fxcrt/bytestring_unittest.cpp
@@ -603,27 +603,27 @@
   EXPECT_EQ("", empty);
 }
 
-TEST(ByteString, Mid) {
+TEST(ByteString, Substr) {
   ByteString fred("FRED");
-  EXPECT_EQ("", fred.Mid(0, 0));
-  EXPECT_EQ("", fred.Mid(3, 0));
-  EXPECT_EQ("FRED", fred.Mid(0, 4));
-  EXPECT_EQ("RED", fred.Mid(1, 3));
-  EXPECT_EQ("ED", fred.Mid(2, 2));
-  EXPECT_EQ("D", fred.Mid(3, 1));
-  EXPECT_EQ("F", fred.Mid(0, 1));
-  EXPECT_EQ("R", fred.Mid(1, 1));
-  EXPECT_EQ("E", fred.Mid(2, 1));
-  EXPECT_EQ("D", fred.Mid(3, 1));
-  EXPECT_EQ("FR", fred.Mid(0, 2));
-  EXPECT_EQ("FRED", fred.Mid(0, 4));
-  EXPECT_EQ("", fred.Mid(0, 10));
+  EXPECT_EQ("", fred.Substr(0, 0));
+  EXPECT_EQ("", fred.Substr(3, 0));
+  EXPECT_EQ("FRED", fred.Substr(0, 4));
+  EXPECT_EQ("RED", fred.Substr(1, 3));
+  EXPECT_EQ("ED", fred.Substr(2, 2));
+  EXPECT_EQ("D", fred.Substr(3, 1));
+  EXPECT_EQ("F", fred.Substr(0, 1));
+  EXPECT_EQ("R", fred.Substr(1, 1));
+  EXPECT_EQ("E", fred.Substr(2, 1));
+  EXPECT_EQ("D", fred.Substr(3, 1));
+  EXPECT_EQ("FR", fred.Substr(0, 2));
+  EXPECT_EQ("FRED", fred.Substr(0, 4));
+  EXPECT_EQ("", fred.Substr(0, 10));
 
-  EXPECT_EQ("RED", fred.Mid(1, 3));
-  EXPECT_EQ("", fred.Mid(4, 1));
+  EXPECT_EQ("RED", fred.Substr(1, 3));
+  EXPECT_EQ("", fred.Substr(4, 1));
 
   ByteString empty;
-  EXPECT_EQ("", empty.Mid(0, 0));
+  EXPECT_EQ("", empty.Substr(0, 0));
 }
 
 TEST(ByteString, Left) {
@@ -1260,34 +1260,34 @@
   EXPECT_EQ(2u, result.value());
 }
 
-TEST(ByteStringView, Mid) {
+TEST(ByteStringView, Substr) {
   ByteStringView null_string;
-  EXPECT_EQ(null_string, null_string.Mid(0, 1));
-  EXPECT_EQ(null_string, null_string.Mid(1, 1));
+  EXPECT_EQ(null_string, null_string.Substr(0, 1));
+  EXPECT_EQ(null_string, null_string.Substr(1, 1));
 
   ByteStringView empty_string("");
-  EXPECT_EQ("", empty_string.Mid(0, 1));
-  EXPECT_EQ("", empty_string.Mid(1, 1));
+  EXPECT_EQ("", empty_string.Substr(0, 1));
+  EXPECT_EQ("", empty_string.Substr(1, 1));
 
   ByteStringView single_character("a");
-  EXPECT_EQ("", single_character.Mid(0, 0));
-  EXPECT_EQ(single_character, single_character.Mid(0, 1));
-  EXPECT_EQ("", single_character.Mid(1, 0));
-  EXPECT_EQ("", single_character.Mid(1, 1));
+  EXPECT_EQ("", single_character.Substr(0, 0));
+  EXPECT_EQ(single_character, single_character.Substr(0, 1));
+  EXPECT_EQ("", single_character.Substr(1, 0));
+  EXPECT_EQ("", single_character.Substr(1, 1));
 
   ByteStringView longer_string("abcdef");
-  EXPECT_EQ(longer_string, longer_string.Mid(0, 6));
-  EXPECT_EQ("", longer_string.Mid(0, 187));
+  EXPECT_EQ(longer_string, longer_string.Substr(0, 6));
+  EXPECT_EQ("", longer_string.Substr(0, 187));
 
   ByteStringView leading_substring("ab");
-  EXPECT_EQ(leading_substring, longer_string.Mid(0, 2));
+  EXPECT_EQ(leading_substring, longer_string.Substr(0, 2));
 
   ByteStringView middle_substring("bcde");
-  EXPECT_EQ(middle_substring, longer_string.Mid(1, 4));
+  EXPECT_EQ(middle_substring, longer_string.Substr(1, 4));
 
   ByteStringView trailing_substring("ef");
-  EXPECT_EQ(trailing_substring, longer_string.Mid(4, 2));
-  EXPECT_EQ("", longer_string.Mid(4, 3));
+  EXPECT_EQ(trailing_substring, longer_string.Substr(4, 2));
+  EXPECT_EQ("", longer_string.Substr(4, 3));
 }
 
 TEST(ByteStringView, TrimmedRight) {
diff --git a/core/fxcrt/string_view_template.h b/core/fxcrt/string_view_template.h
index 4a7c4a6..135b5a3 100644
--- a/core/fxcrt/string_view_template.h
+++ b/core/fxcrt/string_view_template.h
@@ -21,7 +21,7 @@
 
 // An immutable string with caller-provided storage which must outlive the
 // string itself. These are not necessarily nul-terminated, so that substring
-// extraction (via the Mid(), Left(), and Right() methods) is copy-free.
+// extraction (via the Substr(), Left(), and Right() methods) is copy-free.
 //
 // String view arguments should be passed by value, since they are small,
 // rather than const-ref, even if they are not modified.
@@ -197,7 +197,7 @@
 
   bool Contains(CharType ch) const { return Find(ch).has_value(); }
 
-  StringViewTemplate Mid(size_t first, size_t count) const {
+  StringViewTemplate Substr(size_t first, size_t count) const {
     if (!m_Span.data())
       return StringViewTemplate();
 
@@ -216,13 +216,13 @@
   StringViewTemplate Left(size_t count) const {
     if (count == 0 || !IsValidLength(count))
       return StringViewTemplate();
-    return Mid(0, count);
+    return Substr(0, count);
   }
 
   StringViewTemplate Right(size_t count) const {
     if (count == 0 || !IsValidLength(count))
       return StringViewTemplate();
-    return Mid(GetLength() - count, count);
+    return Substr(GetLength() - count, count);
   }
 
   StringViewTemplate TrimmedRight(CharType ch) const {
diff --git a/core/fxcrt/widestring.cpp b/core/fxcrt/widestring.cpp
index 8da9e8d..79fe3b0 100644
--- a/core/fxcrt/widestring.cpp
+++ b/core/fxcrt/widestring.cpp
@@ -694,7 +694,7 @@
   return result;
 }
 
-WideString WideString::Mid(size_t first, size_t count) const {
+WideString WideString::Substr(size_t first, size_t count) const {
   if (!m_pData)
     return WideString();
 
@@ -718,13 +718,13 @@
 WideString WideString::Left(size_t count) const {
   if (count == 0 || !IsValidLength(count))
     return WideString();
-  return Mid(0, count);
+  return Substr(0, count);
 }
 
 WideString WideString::Right(size_t count) const {
   if (count == 0 || !IsValidLength(count))
     return WideString();
-  return Mid(GetLength() - count, count);
+  return Substr(GetLength() - count, count);
 }
 
 void WideString::AllocCopy(WideString& dest,
diff --git a/core/fxcrt/widestring.h b/core/fxcrt/widestring.h
index a9b10ce..10a86ba 100644
--- a/core/fxcrt/widestring.h
+++ b/core/fxcrt/widestring.h
@@ -150,7 +150,7 @@
   int Compare(const WideString& str) const;
   int CompareNoCase(const wchar_t* str) const;
 
-  WideString Mid(size_t first, size_t count) const;
+  WideString Substr(size_t first, size_t count) const;
   WideString Left(size_t count) const;
   WideString Right(size_t count) const;
 
diff --git a/core/fxcrt/widestring_unittest.cpp b/core/fxcrt/widestring_unittest.cpp
index 8d25476..b71c937 100644
--- a/core/fxcrt/widestring_unittest.cpp
+++ b/core/fxcrt/widestring_unittest.cpp
@@ -611,27 +611,27 @@
   EXPECT_EQ(L"", empty);
 }
 
-TEST(WideString, Mid) {
+TEST(WideString, Substr) {
   WideString fred(L"FRED");
-  EXPECT_EQ(L"", fred.Mid(0, 0));
-  EXPECT_EQ(L"", fred.Mid(3, 0));
-  EXPECT_EQ(L"FRED", fred.Mid(0, 4));
-  EXPECT_EQ(L"RED", fred.Mid(1, 3));
-  EXPECT_EQ(L"ED", fred.Mid(2, 2));
-  EXPECT_EQ(L"D", fred.Mid(3, 1));
-  EXPECT_EQ(L"F", fred.Mid(0, 1));
-  EXPECT_EQ(L"R", fred.Mid(1, 1));
-  EXPECT_EQ(L"E", fred.Mid(2, 1));
-  EXPECT_EQ(L"D", fred.Mid(3, 1));
-  EXPECT_EQ(L"FR", fred.Mid(0, 2));
-  EXPECT_EQ(L"FRED", fred.Mid(0, 4));
-  EXPECT_EQ(L"", fred.Mid(0, 10));
+  EXPECT_EQ(L"", fred.Substr(0, 0));
+  EXPECT_EQ(L"", fred.Substr(3, 0));
+  EXPECT_EQ(L"FRED", fred.Substr(0, 4));
+  EXPECT_EQ(L"RED", fred.Substr(1, 3));
+  EXPECT_EQ(L"ED", fred.Substr(2, 2));
+  EXPECT_EQ(L"D", fred.Substr(3, 1));
+  EXPECT_EQ(L"F", fred.Substr(0, 1));
+  EXPECT_EQ(L"R", fred.Substr(1, 1));
+  EXPECT_EQ(L"E", fred.Substr(2, 1));
+  EXPECT_EQ(L"D", fred.Substr(3, 1));
+  EXPECT_EQ(L"FR", fred.Substr(0, 2));
+  EXPECT_EQ(L"FRED", fred.Substr(0, 4));
+  EXPECT_EQ(L"", fred.Substr(0, 10));
 
-  EXPECT_EQ(L"", fred.Mid(1, 4));
-  EXPECT_EQ(L"", fred.Mid(4, 1));
+  EXPECT_EQ(L"", fred.Substr(1, 4));
+  EXPECT_EQ(L"", fred.Substr(4, 1));
 
   WideString empty;
-  EXPECT_EQ(L"", empty.Mid(0, 0));
+  EXPECT_EQ(L"", empty.Substr(0, 0));
 }
 
 TEST(WideString, Left) {