diff --git a/sources/SquirrelInputController.swift b/sources/SquirrelInputController.swift
index d8c9e7352..bad53d9f1 100644
--- a/sources/SquirrelInputController.swift
+++ b/sources/SquirrelInputController.swift
@@ -457,27 +457,48 @@ private extension SquirrelInputController {
 
       if inlineCandidate {
         var candidatePreview = ctx.commit_text_preview.map { String(cString: $0) } ?? ""
+        let endOfCandidatePreview = candidatePreview.endIndex
         if inlinePreedit {
+          // 左移光標後的情形：
+          // preedit:             ^已選某些字[xiang zuo yi dong]|guangbiao$
+          // commit_text_preview: ^已選某些字向左移動$
+          // candidate_preview:   ^已選某些字[向左移動]|guangbiao$
+          // 繼續翻頁至指定更短字詞的情形：
+          // preedit:             ^已選某些字[xiang zuo]yidong|guangbiao$
+          // commit_text_preview: ^已選某些字向左yidong$
+          // candidate_preview:   ^已選某些字[向左]yidong|guangbiao$
+          // 光標移至當前段落最左端的情形：
+          // preedit:             ^已選某些字|[xiang zuo yi dong guang biao]$
+          // commit_text_preview: ^已選某些字向左移動光標$
+          // candidate_preview:   ^已選某些字|[向左移動光標]$
+          // 討論：
+          // preedit 與 commit_text_preview 中“已選某些字”部分一致
+          // 因此，選中範圍即正在翻譯的碼段“向左移動”中，兩者的 start 值一致
+          // 光標位置的範圍是 start ..= endOfCandidatePreview
           if caretPos >= end && caretPos < preedit.endIndex {
+            // 從 preedit 截取光標後未翻譯的編碼“guangbiao”
             candidatePreview += preedit[caretPos...]
           }
-          show(preedit: candidatePreview,
-               selRange: NSRange(location: start.utf16Offset(in: candidatePreview), length: candidatePreview.utf16.distance(from: start, to: candidatePreview.endIndex)),
-               caretPos: candidatePreview.utf16.count - max(0, preedit.utf16.distance(from: caretPos, to: preedit.endIndex)))
         } else {
-          if end < caretPos && start < caretPos {
-            candidatePreview = String(candidatePreview[..<candidatePreview.index(candidatePreview.endIndex, offsetBy: -max(0, preedit.distance(from: end, to: caretPos)))])
-          } else if end < preedit.endIndex && caretPos <= start {
-            candidatePreview = String(candidatePreview[..<candidatePreview.index(candidatePreview.endIndex, offsetBy: -min(candidatePreview.count, max(0, preedit.distance(from: end, to: preedit.endIndex))))])
-          }
-          
-          let selStart = candidatePreview.isEmpty ? 0 : start.utf16Offset(in: candidatePreview)
-          let selLength = candidatePreview.utf16.count - selStart
-          
-          show(preedit: candidatePreview,
-               selRange: NSRange(location: selStart, length: selLength),
-               caretPos: candidatePreview.utf16.count)
+          // 翻頁至指定更短字詞的情形：
+          // preedit:             ^已選某些字[xiang zuo]yidong|guangbiao$
+          // commit_text_preview: ^已選某些字向左yidongguangbiao$
+          // candidate_preview:   ^已選某些字[向左???]|$
+          // 光標移至當前段落最左端，繼續翻頁至指定更短字詞的情形：
+          // preedit:             ^已選某些字|[xiang zuo]yidongguangbiao$
+          // commit_text_preview: ^已選某些字向左yidongguangbiao$
+          // candidate_preview:   ^已選某些字|[向左]???$
+          // FIXME: add librime APIs to support preview candidate without remaining code.
         }
+        // preedit can contain additional prompt text before start:
+        // ^(prompt)[selection]$
+        let start = min(start, candidatePreview.endIndex)
+        // caret can be either before or after the selected range.
+        let caretPos = caretPos <= start ? caretPos : endOfCandidatePreview
+        show(preedit: candidatePreview,
+             selRange: NSRange(location: start.utf16Offset(in: candidatePreview),
+                               length: candidatePreview.utf16.distance(from: start, to: candidatePreview.endIndex)),
+             caretPos: caretPos.utf16Offset(in: candidatePreview))
       } else {
         if inlinePreedit {
           show(preedit: preedit, selRange: NSRange(location: start.utf16Offset(in: preedit), length: preedit.utf16.distance(from: start, to: end)), caretPos: caretPos.utf16Offset(in: preedit))