diff --git a/src/difference/ArcanistDiffUtils.php b/src/difference/ArcanistDiffUtils.php
--- a/src/difference/ArcanistDiffUtils.php
+++ b/src/difference/ArcanistDiffUtils.php
@@ -82,95 +82,6 @@
     return self::computeIntralineEdits($o, $n, $max_glyphs);
   }
 
-  public static function applyIntralineDiff($str, $intra_stack) {
-    $buf = '';
-    $p = $s = $e = 0; // position, start, end
-    $highlight = $tag = $ent = false;
-    $highlight_o = '<span class="bright">';
-    $highlight_c = '</span>';
-
-    $depth_in = '<span class="depth-in">';
-    $depth_out = '<span class="depth-out">';
-
-    $is_html = false;
-    if ($str instanceof PhutilSafeHTML) {
-      $is_html = true;
-      $str = $str->getHTMLContent();
-    }
-
-    $n = strlen($str);
-    for ($i = 0; $i < $n; $i++) {
-
-      if ($p == $e) {
-        do {
-          if (empty($intra_stack)) {
-            $buf .= substr($str, $i);
-            break 2;
-          }
-          $stack = array_shift($intra_stack);
-          $s = $e;
-          $e += $stack[1];
-        } while ($stack[0] === 0);
-
-        switch ($stack[0]) {
-          case '>':
-            $open_tag = $depth_in;
-            break;
-          case '<':
-            $open_tag = $depth_out;
-            break;
-          default:
-            $open_tag = $highlight_o;
-            break;
-        }
-      }
-
-      if (!$highlight && !$tag && !$ent && $p == $s) {
-        $buf .= $open_tag;
-        $highlight = true;
-      }
-
-      if ($str[$i] == '<') {
-        $tag = true;
-        if ($highlight) {
-          $buf .= $highlight_c;
-        }
-      }
-
-      if (!$tag) {
-        if ($str[$i] == '&') {
-          $ent = true;
-        }
-        if ($ent && $str[$i] == ';') {
-          $ent = false;
-        }
-        if (!$ent) {
-          $p++;
-        }
-      }
-
-      $buf .= $str[$i];
-
-      if ($tag && $str[$i] == '>') {
-        $tag = false;
-        if ($highlight) {
-          $buf .= $open_tag;
-        }
-      }
-
-      if ($highlight && ($p == $e || $i == $n - 1)) {
-        $buf .= $highlight_c;
-        $highlight = false;
-      }
-    }
-
-    if ($is_html) {
-      return phutil_safe_html($buf);
-    }
-
-    return $buf;
-  }
-
   private static function collapseIntralineRuns($runs) {
     $count = count($runs);
     for ($ii = 0; $ii < $count - 1; $ii++) {