diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -5789,6 +5789,8 @@
     'PhutilTranslatedHTMLTestCase' => 'infrastructure/markup/__tests__/PhutilTranslatedHTMLTestCase.php',
     'PhutilTwitchAuthAdapter' => 'applications/auth/adapter/PhutilTwitchAuthAdapter.php',
     'PhutilTwitterAuthAdapter' => 'applications/auth/adapter/PhutilTwitterAuthAdapter.php',
+    'PhutilURIHelper' => 'infrastructure/parser/PhutilURIHelper.php',
+    'PhutilURIHelperTestCase' => 'infrastructure/parser/__tests__/PhutilURIHelperTestCase.php',
     'PhutilWordPressAuthAdapter' => 'applications/auth/adapter/PhutilWordPressAuthAdapter.php',
     'PhutilXHPASTSyntaxHighlighter' => 'infrastructure/markup/syntax/highlighter/PhutilXHPASTSyntaxHighlighter.php',
     'PhutilXHPASTSyntaxHighlighterFuture' => 'infrastructure/markup/syntax/highlighter/xhpast/PhutilXHPASTSyntaxHighlighterFuture.php',
@@ -12675,6 +12677,8 @@
     'PhutilTranslatedHTMLTestCase' => 'PhutilTestCase',
     'PhutilTwitchAuthAdapter' => 'PhutilOAuthAuthAdapter',
     'PhutilTwitterAuthAdapter' => 'PhutilOAuth1AuthAdapter',
+    'PhutilURIHelper' => 'Phobject',
+    'PhutilURIHelperTestCase' => 'PhabricatorTestCase',
     'PhutilWordPressAuthAdapter' => 'PhutilOAuthAuthAdapter',
     'PhutilXHPASTSyntaxHighlighter' => 'Phobject',
     'PhutilXHPASTSyntaxHighlighterFuture' => 'FutureProxy',
diff --git a/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php b/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php
--- a/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php
+++ b/src/infrastructure/markup/markuprule/PhutilRemarkupDocumentLinkRule.php
@@ -44,16 +44,15 @@
   protected function renderHyperlink($link, $name) {
     $engine = $this->getEngine();
 
-    $is_anchor = false;
-    if (strncmp($link, '/', 1) == 0) {
+    $uri = new PhutilURIHelper($link);
+    $is_anchor = $uri->isAnchor();
+    if ($uri->isStartingWithSlash()) {
       $base = phutil_string_cast($engine->getConfig('uri.base'));
       $base = rtrim($base, '/');
       $link = $base.$link;
-    } else if (strncmp($link, '#', 1) == 0) {
+    } else if ($is_anchor) {
       $here = $engine->getConfig('uri.here');
       $link = $here.$link;
-
-      $is_anchor = true;
     }
 
     if ($engine->isTextMode()) {
@@ -76,7 +75,8 @@
       return $name;
     }
 
-    $same_window = $engine->getConfig('uri.same-window', false);
+    $is_self = $uri->isSelf();
+    $same_window = $engine->getConfig('uri.same-window', $is_self);
     if ($same_window) {
       $target = null;
     } else {
@@ -92,7 +92,7 @@
       'a',
       array(
         'href' => $link,
-        'class' => 'remarkup-link',
+        'class' => $this->getRemarkupLinkClass($is_self),
         'target' => $target,
         'rel' => 'noreferrer',
       ),
diff --git a/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php b/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php
--- a/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php
+++ b/src/infrastructure/markup/markuprule/PhutilRemarkupHyperlinkRule.php
@@ -116,7 +116,9 @@
 
     $engine = $this->getEngine();
 
-    $same_window = $engine->getConfig('uri.same-window', false);
+    $uri = new PhutilURIHelper($link);
+    $is_self = $uri->isSelf();
+    $same_window = $engine->getConfig('uri.same-window', $is_self);
     if ($same_window) {
       $target = null;
     } else {
@@ -127,7 +129,7 @@
       'a',
       array(
         'href' => $link,
-        'class' => 'remarkup-link',
+        'class' => $this->getRemarkupLinkClass($is_self),
         'target' => $target,
         'rel' => 'noreferrer',
       ),
diff --git a/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php b/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php
--- a/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php
+++ b/src/infrastructure/markup/markuprule/PhutilRemarkupRule.php
@@ -106,4 +106,20 @@
     return (strpos($text, PhutilRemarkupBlockStorage::MAGIC_BYTE) === false);
   }
 
+  /**
+   * Get the CSS class="" attribute for a Remarkup link.
+   * It's just "remarkup-link" for all cases, plus the possibility for
+   * designers to style external links differently.
+   * @param  boolean $is_internal Whenever the link was internal or not.
+   * @return string
+   */
+  protected function getRemarkupLinkClass($is_internal) {
+    // Allow developers to style esternal links differently
+    $classes = array('remarkup-link');
+    if (!$is_internal) {
+      $classes[] = 'remarkup-link-ext';
+    }
+    return implode(' ', $classes);
+  }
+
 }
diff --git a/src/infrastructure/parser/PhutilURIHelper.php b/src/infrastructure/parser/PhutilURIHelper.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/parser/PhutilURIHelper.php
@@ -0,0 +1,70 @@
+<?php
+
+/**
+ * A simple wrapper for PhutilURI, to be aware of the
+ * relative/absolute context, and other minor things.
+ */
+final class PhutilURIHelper extends Phobject {
+
+  /**
+   * String version of your original URI.
+   * @var string
+   */
+  private $uriStr;
+
+  /**
+   * Structured version of your URI.
+   * @var PhutilURI
+   */
+  private $phutilUri;
+
+  /**
+   * Constructor accepting a string (partial or relative URIs), or a PhutilURI.
+   * @param string|PhutilURI $uri
+   */
+  public function __construct($uri) {
+    $this->uriStr = phutil_string_cast($uri);
+    $this->phutilUri = new PhutilURI($uri);
+  }
+
+  /**
+   * Check if the URI points to Phorge itself.
+   * @return bool
+   */
+  public function isSelf() {
+    return PhabricatorEnv::isSelfURI($this->phutilUri);
+  }
+
+  /**
+   * Check whenever an URI is just a simple fragment without path and protocol.
+   * @return bool
+   */
+  public function isAnchor() {
+    return $this->isStartingWithChar('#');
+  }
+
+  /**
+   * Check whenever an URI starts with a slash (no protocol, etc.)
+   * @return bool
+   */
+  public function isStartingWithSlash() {
+    return $this->isStartingWithChar('/');
+  }
+
+  /**
+   * A sane default.
+   */
+  public function __toString() {
+    return $this->uriStr;
+  }
+
+  /**
+   * Check whenever the URI starts with the provided character.
+   * @param string $char String that MUST have length of 1.
+   * @return boolean
+   */
+  private function isStartingWithChar($char) {
+    return strncmp($this->uriStr, $char, 1) === 0;
+  }
+
+}
diff --git a/src/infrastructure/parser/__tests__/PhutilURIHelperTestCase.php b/src/infrastructure/parser/__tests__/PhutilURIHelperTestCase.php
new file mode 100644
--- /dev/null
+++ b/src/infrastructure/parser/__tests__/PhutilURIHelperTestCase.php
@@ -0,0 +1,63 @@
+<?php
+
+final class PhutilURIHelperTestCase extends PhabricatorTestCase {
+
+ public function testPhutilURIHelper() {
+
+    // Every row is a test. Every column is:
+    // - 0: name of the test
+    // - 1: test input value
+    // - 2: is the URI pointing to Phorge itself?
+    // - 3: is the URI an anchor? (no domain, no protocol)
+    // - 4: is the URI starting with a slash? (no domain, no protocol)
+    $tests = array(
+      array('internal anchor', '#asd', true, true, false),
+      array('internal relative dir', '/foo/', true, false, true),
+      array('internal relative dir also', 'foo/', true, false, false),
+      array('internal root dir', '/', true, false, true),
+      array('internal root dir', './', true, false, false),
+      array('internal root dir', '../', true, false, false),
+      array('internal root dir', '/#asd', true, false, true),
+      array('external', 'https://gnu.org/', false, false, false),
+      array('external anchor', 'https://gnu.org/#asd', false, false, false),
+    );
+
+    // Add additional self-tests if base URI is available.
+    $base = PhabricatorEnv::getEnvConfigIfExists('phabricator.base-uri');
+    if ($base) {
+      $domain = id(new PhutilURI($base))->getDomain();
+      $tests[] = array('base uri', $base, true, false, false);
+      $tests[] = array('base uri anchor', "{$base}#asd", true, false, false);
+    }
+
+    foreach ($tests as $test) {
+      $name = $test[0];
+      $uri = $test[1];
+      $is_self = $test[2];
+      $is_anchor = $test[3];
+      $is_slash = $test[4];
+
+      // Test input variants for the constructor of PhutilURIHelper.
+      $uri_variants = array(
+        $uri,
+        new PhutilURI($uri),
+      );
+      foreach ($uri_variants as $variant_uri) {
+
+        $test_name = pht("test %s value '%s' (from '%s' type %s)",
+          $name, $variant_uri, $uri, phutil_describe_type($variant_uri));
+
+        $uri = new PhutilURIHelper($variant_uri);
+
+        $this->assertEqual($is_self, $uri->isSelf(),
+          pht('%s - points to myself', $test_name));
+
+        $this->assertEqual($is_anchor, $uri->isAnchor(),
+          pht('%s - is just an anchor', $test_name));
+
+        $this->assertEqual($is_slash, $uri->isStartingWithSlash(),
+          pht('%s - is starting with slash', $test_name));
+      }
+    }
+  }
+}