diff --git a/core/fxcrt/widestring.cpp b/core/fxcrt/widestring.cpp
index 234270e..d699b42 100644
--- a/core/fxcrt/widestring.cpp
+++ b/core/fxcrt/widestring.cpp
@@ -635,7 +635,22 @@
   return m_pData ? m_pData->m_nRefs : 0;
 }
 
-// static
+bool WideString::IsASCII() const {
+  for (wchar_t wc : *this) {
+    if (wc <= 0 || wc > 127)  // Questionable signedness of wchar_t.
+      return false;
+  }
+  return true;
+}
+
+ByteString WideString::ToASCII() const {
+  ByteString result;
+  result.Reserve(GetLength());
+  for (wchar_t wc : *this)
+    result.InsertAtBack(static_cast<char>(wc & 0x7f));
+  return result;
+}
+
 ByteString WideString::ToDefANSI() const {
   int src_len = GetLength();
   int dest_len = FXSYS_WideCharToMultiByte(
@@ -864,6 +879,15 @@
 }
 
 // static
+WideString WideString::FromASCII(const ByteStringView& bstr) {
+  WideString result;
+  result.Reserve(bstr.GetLength());
+  for (char c : bstr)
+    result.InsertAtBack(static_cast<wchar_t>(c & 0x7f));
+  return result;
+}
+
+// static
 WideString WideString::FromDefANSI(const ByteStringView& bstr) {
   int src_len = bstr.GetLength();
   int dest_len = FXSYS_MultiByteToWideChar(
diff --git a/core/fxcrt/widestring.h b/core/fxcrt/widestring.h
index 70339ff..87e886c 100644
--- a/core/fxcrt/widestring.h
+++ b/core/fxcrt/widestring.h
@@ -60,6 +60,7 @@
 
   ~WideString();
 
+  static WideString FromASCII(const ByteStringView& str) WARN_UNUSED_RESULT;
   static WideString FromDefANSI(const ByteStringView& str) WARN_UNUSED_RESULT;
   static WideString FromUTF8(const ByteStringView& str) WARN_UNUSED_RESULT;
   static WideString FromUTF16LE(const unsigned short* str,
@@ -191,6 +192,8 @@
   size_t Replace(const WideStringView& pOld, const WideStringView& pNew);
   size_t Remove(wchar_t ch);
 
+  bool IsASCII() const;
+  ByteString ToASCII() const;
   ByteString ToDefANSI() const;
   ByteString ToUTF8() const;
 
diff --git a/core/fxcrt/widestring_unittest.cpp b/core/fxcrt/widestring_unittest.cpp
index 2d8a676..5efb556 100644
--- a/core/fxcrt/widestring_unittest.cpp
+++ b/core/fxcrt/widestring_unittest.cpp
@@ -1001,6 +1001,29 @@
   }
 }
 
+TEST(WideString, IsASCII) {
+  EXPECT_TRUE(WideString(L"xy\u007fz").IsASCII());
+  EXPECT_FALSE(WideString(L"xy\u0080z").IsASCII());
+  EXPECT_FALSE(WideString(L"xy\u2041z").IsASCII());
+}
+
+TEST(WideString, ToASCII) {
+  const char* kResult =
+      "x"
+      "\x02"
+      "\x7f"
+      "\x22"
+      "\x0c"
+      "y";
+  EXPECT_EQ(kResult, WideString(L"x"
+                                L"\u0082"
+                                L"\u00ff"
+                                L"\u0122"
+                                L"\u208c"
+                                L"y")
+                         .ToASCII());
+}
+
 TEST(WideString, ToDefANSI) {
   EXPECT_EQ("", WideString().ToDefANSI());
 #if _FX_PLATFORM_ == _FX_PLATFORM_WINDOWS_
@@ -1027,7 +1050,20 @@
                          .ToDefANSI());
 }
 
-TEST(WideString, FromLocal) {
+TEST(WideString, FromASCII) {
+  EXPECT_EQ(L"", WideString::FromDefANSI(ByteStringView()));
+  const wchar_t* kResult =
+      L"x"
+      L"\u0002"
+      L"\u007f"
+      L"y";
+  EXPECT_EQ(kResult, WideString::FromASCII("x"
+                                           "\x82"
+                                           "\xff"
+                                           "y"));
+}
+
+TEST(WideString, FromDefANSI) {
   EXPECT_EQ(L"", WideString::FromDefANSI(ByteStringView()));
 #if _FX_PLATFORM_ == _FX_PLATFORM_WINDOWS_
   const wchar_t* kResult =