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
@@ -2295,6 +2295,7 @@
     'PhabricatorProjectInterface' => 'applications/project/interface/PhabricatorProjectInterface.php',
     'PhabricatorProjectListController' => 'applications/project/controller/PhabricatorProjectListController.php',
     'PhabricatorProjectMemberOfProjectEdgeType' => 'applications/project/edge/PhabricatorProjectMemberOfProjectEdgeType.php',
+    'PhabricatorProjectMembersDatasource' => 'applications/project/typeahead/PhabricatorProjectMembersDatasource.php',
     'PhabricatorProjectMembersEditController' => 'applications/project/controller/PhabricatorProjectMembersEditController.php',
     'PhabricatorProjectMembersRemoveController' => 'applications/project/controller/PhabricatorProjectMembersRemoveController.php',
     'PhabricatorProjectMoveController' => 'applications/project/controller/PhabricatorProjectMoveController.php',
@@ -2627,6 +2628,7 @@
     'PhabricatorTypeaheadCompositeDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php',
     'PhabricatorTypeaheadDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php',
     'PhabricatorTypeaheadDatasourceController' => 'applications/typeahead/controller/PhabricatorTypeaheadDatasourceController.php',
+    'PhabricatorTypeaheadInvalidTokenException' => 'applications/typeahead/exception/PhabricatorTypeaheadInvalidTokenException.php',
     'PhabricatorTypeaheadModularDatasourceController' => 'applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php',
     'PhabricatorTypeaheadMonogramDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadMonogramDatasource.php',
     'PhabricatorTypeaheadNoOwnerDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadNoOwnerDatasource.php',
@@ -2634,6 +2636,7 @@
     'PhabricatorTypeaheadResult' => 'applications/typeahead/storage/PhabricatorTypeaheadResult.php',
     'PhabricatorTypeaheadRuntimeCompositeDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadRuntimeCompositeDatasource.php',
     'PhabricatorTypeaheadTokenView' => 'applications/typeahead/view/PhabricatorTypeaheadTokenView.php',
+    'PhabricatorTypeaheadUserParameterizedDatasource' => 'applications/typeahead/datasource/PhabricatorTypeaheadUserParameterizedDatasource.php',
     'PhabricatorUIConfigOptions' => 'applications/config/option/PhabricatorUIConfigOptions.php',
     'PhabricatorUIExample' => 'applications/uiexample/examples/PhabricatorUIExample.php',
     'PhabricatorUIExampleRenderController' => 'applications/uiexample/controller/PhabricatorUIExampleRenderController.php',
@@ -2671,6 +2674,7 @@
     'PhabricatorUsersPolicyRule' => 'applications/policy/rule/PhabricatorUsersPolicyRule.php',
     'PhabricatorVCSResponse' => 'applications/repository/response/PhabricatorVCSResponse.php',
     'PhabricatorVeryWowEnglishTranslation' => 'infrastructure/internationalization/translation/PhabricatorVeryWowEnglishTranslation.php',
+    'PhabricatorViewerDatasource' => 'applications/people/typeahead/PhabricatorViewerDatasource.php',
     'PhabricatorWatcherHasObjectEdgeType' => 'applications/transactions/edges/PhabricatorWatcherHasObjectEdgeType.php',
     'PhabricatorWordPressAuthProvider' => 'applications/auth/provider/PhabricatorWordPressAuthProvider.php',
     'PhabricatorWorker' => 'infrastructure/daemon/workers/PhabricatorWorker.php',
@@ -5664,6 +5668,7 @@
     'PhabricatorProjectIcon' => 'Phobject',
     'PhabricatorProjectListController' => 'PhabricatorProjectController',
     'PhabricatorProjectMemberOfProjectEdgeType' => 'PhabricatorEdgeType',
+    'PhabricatorProjectMembersDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorProjectMembersEditController' => 'PhabricatorProjectController',
     'PhabricatorProjectMembersRemoveController' => 'PhabricatorProjectController',
     'PhabricatorProjectMoveController' => 'PhabricatorProjectController',
@@ -6026,12 +6031,14 @@
     'PhabricatorTypeaheadCompositeDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorTypeaheadDatasource' => 'Phobject',
     'PhabricatorTypeaheadDatasourceController' => 'PhabricatorController',
+    'PhabricatorTypeaheadInvalidTokenException' => 'Exception',
     'PhabricatorTypeaheadModularDatasourceController' => 'PhabricatorTypeaheadDatasourceController',
     'PhabricatorTypeaheadMonogramDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorTypeaheadNoOwnerDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorTypeaheadOwnerDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'PhabricatorTypeaheadRuntimeCompositeDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'PhabricatorTypeaheadTokenView' => 'AphrontTagView',
+    'PhabricatorTypeaheadUserParameterizedDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'PhabricatorUIConfigOptions' => 'PhabricatorApplicationConfigOptions',
     'PhabricatorUIExampleRenderController' => 'PhabricatorController',
     'PhabricatorUIExamplesApplication' => 'PhabricatorApplication',
@@ -6081,6 +6088,7 @@
     'PhabricatorUsersPolicyRule' => 'PhabricatorPolicyRule',
     'PhabricatorVCSResponse' => 'AphrontResponse',
     'PhabricatorVeryWowEnglishTranslation' => 'PhutilTranslation',
+    'PhabricatorViewerDatasource' => 'PhabricatorTypeaheadDatasource',
     'PhabricatorWatcherHasObjectEdgeType' => 'PhabricatorEdgeType',
     'PhabricatorWordPressAuthProvider' => 'PhabricatorOAuth2AuthProvider',
     'PhabricatorWorkerActiveTask' => 'PhabricatorWorkerTask',
diff --git a/src/applications/differential/query/DifferentialRevisionSearchEngine.php b/src/applications/differential/query/DifferentialRevisionSearchEngine.php
--- a/src/applications/differential/query/DifferentialRevisionSearchEngine.php
+++ b/src/applications/differential/query/DifferentialRevisionSearchEngine.php
@@ -67,7 +67,11 @@
       ->needDrafts(true)
       ->needRelationships(true);
 
+    $datasource = id(new PhabricatorTypeaheadUserParameterizedDatasource())
+      ->setViewer($this->requireViewer());
+
     $responsible_phids = $saved->getParameter('responsiblePHIDs', array());
+    $responsible_phids = $datasource->evaluateTokens($responsible_phids);
     if ($responsible_phids) {
       $query->withResponsibleUsers($responsible_phids);
     }
@@ -129,7 +133,7 @@
         id(new AphrontFormTokenizerControl())
           ->setLabel(pht('Responsible Users'))
           ->setName('responsibles')
-          ->setDatasource(new PhabricatorPeopleDatasource())
+          ->setDatasource(new PhabricatorTypeaheadUserParameterizedDatasource())
           ->setValue($responsible_phids))
       ->appendControl(
         id(new AphrontFormTokenizerControl())
@@ -208,7 +212,7 @@
     switch ($query_key) {
       case 'active':
         return $query
-          ->setParameter('responsiblePHIDs', array($viewer->getPHID()))
+          ->setParameter('responsiblePHIDs', array('viewer()'))
           ->setParameter('status', DifferentialRevisionQuery::STATUS_OPEN);
       case 'authored':
         return $query
diff --git a/src/applications/harbormaster/query/HarbormasterBuildPlanQuery.php b/src/applications/harbormaster/query/HarbormasterBuildPlanQuery.php
--- a/src/applications/harbormaster/query/HarbormasterBuildPlanQuery.php
+++ b/src/applications/harbormaster/query/HarbormasterBuildPlanQuery.php
@@ -93,7 +93,7 @@
     );
   }
 
-  public function getPagingValueMap($cursor, array $keys) {
+  protected function getPagingValueMap($cursor, array $keys) {
     $plan = $this->loadCursorObject($cursor);
     return array(
       'id' => $plan->getID(),
diff --git a/src/applications/macro/query/PhabricatorMacroQuery.php b/src/applications/macro/query/PhabricatorMacroQuery.php
--- a/src/applications/macro/query/PhabricatorMacroQuery.php
+++ b/src/applications/macro/query/PhabricatorMacroQuery.php
@@ -258,7 +258,7 @@
     );
   }
 
-  public function getPagingValueMap($cursor, array $keys) {
+  protected function getPagingValueMap($cursor, array $keys) {
     $macro = $this->loadCursorObject($cursor);
     return array(
       'id' => $macro->getID(),
diff --git a/src/applications/people/query/PhabricatorPeopleQuery.php b/src/applications/people/query/PhabricatorPeopleQuery.php
--- a/src/applications/people/query/PhabricatorPeopleQuery.php
+++ b/src/applications/people/query/PhabricatorPeopleQuery.php
@@ -338,7 +338,7 @@
     );
   }
 
-  public function getPagingValueMap($cursor, array $keys) {
+  protected function getPagingValueMap($cursor, array $keys) {
     $user = $this->loadCursorObject($cursor);
     return array(
       'id' => $user->getID(),
diff --git a/src/applications/people/typeahead/PhabricatorViewerDatasource.php b/src/applications/people/typeahead/PhabricatorViewerDatasource.php
new file mode 100644
--- /dev/null
+++ b/src/applications/people/typeahead/PhabricatorViewerDatasource.php
@@ -0,0 +1,56 @@
+<?php
+
+final class PhabricatorViewerDatasource
+  extends PhabricatorTypeaheadDatasource {
+
+  public function getPlaceholderText() {
+    return pht('Type viewer()...');
+  }
+
+  public function getDatasourceApplicationClass() {
+    return 'PhabricatorPeopleApplication';
+  }
+
+  public function loadResults() {
+    if ($this->getViewer()->getPHID()) {
+      $results = array($this->renderViewerFunctionToken());
+    } else {
+      $results = array();
+    }
+
+    return $this->filterResultsAgainstTokens($results);
+  }
+
+  protected function canEvaluateFunction($function) {
+    if (!$this->getViewer()->getPHID()) {
+      return false;
+    }
+
+    return ($function == 'viewer');
+  }
+
+  protected function evaluateFunction($function, array $argv_list) {
+    $results = array();
+    foreach ($argv_list as $argv) {
+      $results[] = $this->getViewer()->getPHID();
+    }
+    return $results;
+  }
+
+  public function renderFunctionTokens($function, array $argv_list) {
+    $tokens = array();
+    foreach ($argv_list as $argv) {
+      $tokens[] = PhabricatorTypeaheadTokenView::newFromTypeaheadResult(
+        $this->renderViewerFunctionToken());
+    }
+    return $tokens;
+  }
+
+  private function renderViewerFunctionToken() {
+    return $this->newFunctionResult()
+      ->setName(pht('Current Viewer'))
+      ->setPHID('viewer()')
+      ->setUnique(true);
+  }
+
+}
diff --git a/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php b/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php
new file mode 100644
--- /dev/null
+++ b/src/applications/project/typeahead/PhabricatorProjectMembersDatasource.php
@@ -0,0 +1,122 @@
+<?php
+
+final class PhabricatorProjectMembersDatasource
+  extends PhabricatorTypeaheadDatasource {
+
+  public function getPlaceholderText() {
+    return pht('Type members(<project>)...');
+  }
+
+  public function getDatasourceApplicationClass() {
+    return 'PhabricatorProjectApplication';
+  }
+
+  public function loadResults() {
+    $viewer = $this->getViewer();
+    $raw_query = $this->getRawQuery();
+
+    $pattern = $raw_query;
+    if (self::isFunctionToken($raw_query)) {
+      $function = $this->parseFunction($raw_query, $allow_partial = true);
+      if ($function) {
+        $pattern = head($function['argv']);
+      }
+    }
+
+    // Allow users to type "#qa" or "qa" to find "Quality Assurance".
+    $pattern = ltrim($pattern, '#');
+    $tokens = self::tokenizeString($pattern);
+
+    $query = $this->newQuery();
+    if ($tokens) {
+      $query->withNameTokens($tokens);
+    }
+    $projects = $this->executeQuery($query);
+
+    $results = array();
+    foreach ($projects as $project) {
+      $results[] = $this->buildProjectResult($project);
+    }
+
+    return $results;
+  }
+
+  protected function canEvaluateFunction($function) {
+    return ($function == 'members');
+  }
+
+  protected function evaluateFunction($function, array $argv_list) {
+    $phids = array();
+    foreach ($argv_list as $argv) {
+      $phids[] = head($argv);
+    }
+
+    $projects = id(new PhabricatorProjectQuery())
+      ->setViewer($this->getViewer())
+      ->needMembers(true)
+      ->withPHIDs($phids)
+      ->execute();
+
+    $results = array();
+    foreach ($projects as $project) {
+      foreach ($project->getMemberPHIDs() as $phid) {
+        $results[$phid] = $phid;
+      }
+    }
+
+    return array_values($results);
+  }
+
+  public function renderFunctionTokens($function, array $argv_list) {
+    $phids = array();
+    foreach ($argv_list as $argv) {
+      $phids[] = head($argv);
+    }
+
+    $projects = $this->newQuery()
+      ->withPHIDs($phids)
+      ->execute();
+    $projects = mpull($projects, null, 'getPHID');
+
+    $tokens = array();
+    foreach ($phids as $phid) {
+      $project = idx($projects, $phid);
+      if ($project) {
+        $result = $this->buildProjectResult($project);
+        $tokens[] = PhabricatorTypeaheadTokenView::newFromTypeaheadResult(
+          $result);
+      } else {
+        $tokens[] = $this->newInvalidToken(pht('Members: Invalid Project'));
+      }
+    }
+
+    return $tokens;
+  }
+
+  private function newQuery() {
+    return id(new PhabricatorProjectQuery())
+      ->setViewer($this->getViewer())
+      ->needImages(true)
+      ->needSlugs(true);
+  }
+
+  private function buildProjectResult(PhabricatorProject $project) {
+    $closed = null;
+    if ($project->isArchived()) {
+      $closed = pht('Archived');
+    }
+
+    $all_strings = mpull($project->getSlugs(), 'getSlug');
+    $all_strings[] = 'members';
+    $all_strings[] = $project->getName();
+    $all_strings = implode(' ', $all_strings);
+
+    return $this->newFunctionResult()
+      ->setName($all_strings)
+      ->setDisplayName(pht('Members: %s', $project->getName()))
+      ->setURI('/tag/'.$project->getPrimarySlug().'/')
+      ->setPHID('members('.$project->getPHID().')')
+      ->setClosed($closed);
+  }
+
+}
diff --git a/src/applications/search/controller/PhabricatorApplicationSearchController.php b/src/applications/search/controller/PhabricatorApplicationSearchController.php
--- a/src/applications/search/controller/PhabricatorApplicationSearchController.php
+++ b/src/applications/search/controller/PhabricatorApplicationSearchController.php
@@ -165,9 +165,6 @@
     $errors = $engine->getErrors();
     if ($errors) {
       $run_query = false;
-      $errors = id(new PHUIInfoView())
-        ->setTitle(pht('Query Errors'))
-        ->setErrors($errors);
     }
 
     $submit = id(new AphrontFormSubmitControl())
@@ -214,46 +211,58 @@
         $anchor = id(new PhabricatorAnchorView())
           ->setAnchorName('R'));
 
-      $query = $engine->buildQueryFromSavedQuery($saved_query);
+      try {
+        $query = $engine->buildQueryFromSavedQuery($saved_query);
 
-      $pager = $engine->newPagerForSavedQuery($saved_query);
-      $pager->readFromRequest($request);
+        $pager = $engine->newPagerForSavedQuery($saved_query);
+        $pager->readFromRequest($request);
 
-      $objects = $engine->executeQuery($query, $pager);
+        $objects = $engine->executeQuery($query, $pager);
 
-      // TODO: To support Dashboard panels, rendering is moving into
-      // SearchEngines. Move it all the way in and then get rid of this.
+        // TODO: To support Dashboard panels, rendering is moving into
+        // SearchEngines. Move it all the way in and then get rid of this.
 
-      $interface = 'PhabricatorApplicationSearchResultsControllerInterface';
-      if ($parent instanceof $interface) {
-        $list = $parent->renderResultsList($objects, $saved_query);
-      } else {
-        $engine->setRequest($request);
+        $interface = 'PhabricatorApplicationSearchResultsControllerInterface';
+        if ($parent instanceof $interface) {
+          $list = $parent->renderResultsList($objects, $saved_query);
+        } else {
+          $engine->setRequest($request);
 
-        $list = $engine->renderResults(
-          $objects,
-          $saved_query);
-      }
+          $list = $engine->renderResults(
+            $objects,
+            $saved_query);
+        }
 
-      $nav->appendChild($list);
+        $nav->appendChild($list);
 
-      // TODO: This is a bit hacky.
-      if ($list instanceof PHUIObjectItemListView) {
-        $list->setNoDataString(pht('No results found for this query.'));
-        $list->setPager($pager);
-      } else {
-        if ($pager->willShowPagingControls()) {
-          $pager_box = id(new PHUIBoxView())
-            ->addPadding(PHUI::PADDING_MEDIUM)
-            ->addMargin(PHUI::MARGIN_LARGE)
-            ->setBorder(true)
-            ->appendChild($pager);
-          $nav->appendChild($pager_box);
+        // TODO: This is a bit hacky.
+        if ($list instanceof PHUIObjectItemListView) {
+          $list->setNoDataString(pht('No results found for this query.'));
+          $list->setPager($pager);
+        } else {
+          if ($pager->willShowPagingControls()) {
+            $pager_box = id(new PHUIBoxView())
+              ->addPadding(PHUI::PADDING_MEDIUM)
+              ->addMargin(PHUI::MARGIN_LARGE)
+              ->setBorder(true)
+              ->appendChild($pager);
+            $nav->appendChild($pager_box);
+          }
         }
+      } catch (PhabricatorTypeaheadInvalidTokenException $ex) {
+        $errors[] = pht(
+          'This query specifies an invalid parameter. Review the '.
+          'query parameters and correct errors.');
       }
     }
 
     if ($errors) {
+      $errors = id(new PHUIInfoView())
+        ->setTitle(pht('Query Errors'))
+        ->setErrors($errors);
+    }
+
+    if ($errors) {
       $nav->appendChild($errors);
     }
 
diff --git a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
--- a/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
+++ b/src/applications/search/engine/PhabricatorApplicationSearchEngine.php
@@ -383,7 +383,13 @@
       } else if (isset($allow_types[$type])) {
         $phids[] = $item;
       } else {
-        $names[] = $item;
+        if (PhabricatorTypeaheadDatasource::isFunctionToken($item)) {
+          // If this is a function, pass it through unchanged; we'll evaluate
+          // it later.
+          $phids[] = $item;
+        } else {
+          $names[] = $item;
+        }
       }
     }
 
diff --git a/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php b/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php
--- a/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php
+++ b/src/applications/typeahead/controller/PhabricatorTypeaheadModularDatasourceController.php
@@ -49,14 +49,13 @@
         ->setRawQuery($raw_query);
 
       $hard_limit = 1000;
+      $limit = 100;
 
       if ($is_browse) {
         if (!$composite->isBrowsable()) {
           return new Aphront404Response();
         }
 
-        $limit = 10;
-
         if (($offset + $limit) >= $hard_limit) {
           // Offset-based paging is intrinsically slow; hard-cap how far we're
           // willing to go with it.
@@ -140,7 +139,7 @@
 
         $items = array();
         foreach ($results as $result) {
-          $token = PhabricatorTypeaheadTokenView::newForTypeaheadResult(
+          $token = PhabricatorTypeaheadTokenView::newFromTypeaheadResult(
             $result);
 
           // Disable already-selected tokens.
diff --git a/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php b/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php
--- a/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php
+++ b/src/applications/typeahead/datasource/PhabricatorTypeaheadCompositeDatasource.php
@@ -72,6 +72,7 @@
           }
         }
 
+        $source->setViewer($this->getViewer());
         $usable[] = $source;
       }
       $this->usable = $usable;
@@ -80,4 +81,37 @@
     return $this->usable;
   }
 
+
+  protected function canEvaluateFunction($function) {
+    foreach ($this->getUsableDatasources() as $source) {
+      if ($source->canEvaluateFunction($function)) {
+        return true;
+      }
+    }
+
+    return parent::canEvaluateFunction($function);
+  }
+
+
+  protected function evaluateFunction($function, array $argv) {
+    foreach ($this->getUsableDatasources() as $source) {
+      if ($source->canEvaluateFunction($function)) {
+        return $source->evaluateFunction($function, $argv);
+      }
+    }
+
+    return parent::evaluateFunction($function, $argv);
+  }
+
+  public function renderFunctionTokens($function, array $argv_list) {
+    foreach ($this->getUsableDatasources() as $source) {
+      if ($source->canEvaluateFunction($function)) {
+        return $source->renderFunctionTokens($function, $argv_list);
+      }
+    }
+
+    return parent::renderFunctionTokens($function, $argv_list);
+  }
+
+
 }
diff --git a/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php b/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
--- a/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
+++ b/src/applications/typeahead/datasource/PhabricatorTypeaheadDatasource.php
@@ -1,5 +1,8 @@
 <?php
 
+/**
+ * @task functions Token Functions
+ */
 abstract class PhabricatorTypeaheadDatasource extends Phobject {
 
   private $viewer;
@@ -183,4 +186,116 @@
     return $results;
   }
 
+  protected function newFunctionResult() {
+    // TODO: Find a more consistent design.
+    return id(new PhabricatorTypeaheadResult())
+      ->setIcon('fa-magic indigo');
+  }
+
+  public function newInvalidToken($name) {
+    return id(new PhabricatorTypeaheadTokenView())
+      ->setKey(PhabricatorTypeaheadTokenView::KEY_INVALID)
+      ->setValue($name)
+      ->setIcon('fa-exclamation-circle red');
+  }
+
+/* -(  Token Functions  )---------------------------------------------------- */
+
+
+  /**
+   * @task functions
+   */
+  protected function canEvaluateFunction($function) {
+    return false;
+  }
+
+
+  /**
+   * @task functions
+   */
+  protected function evaluateFunction($function, array $argv_list) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+
+  /**
+   * @task functions
+   */
+  public function evaluateTokens(array $tokens) {
+    $results = array();
+    $evaluate = array();
+    foreach ($tokens as $token) {
+      if (!self::isFunctionToken($token)) {
+        $results[] = $token;
+      } else {
+        $evaluate[] = $token;
+      }
+    }
+
+    foreach ($evaluate as $function) {
+      $function = self::parseFunction($function);
+      if (!$function) {
+        throw new PhabricatorTypeaheadInvalidTokenException();
+      }
+
+      $name = $function['name'];
+      $argv = $function['argv'];
+
+      foreach ($this->evaluateFunction($name, array($argv)) as $phid) {
+        $results[] = $phid;
+      }
+    }
+
+    return $results;
+  }
+
+
+  /**
+   * @task functions
+   */
+  public static function isFunctionToken($token) {
+    // We're looking for a "(" so that a string like "members(q" is identified
+    // and parsed as a function call. This allows us to start generating
+    // results immeidately, before the user fully types out "members(quack)".
+    return (strpos($token, '(') !== false);
+  }
+
+
+  /**
+   * @task functions
+   */
+  public function parseFunction($token, $allow_partial = false) {
+    $matches = null;
+
+    if ($allow_partial) {
+      $ok = preg_match('/^([^(]+)\((.*)$/', $token, $matches);
+    } else {
+      $ok = preg_match('/^([^(]+)\((.*)\)$/', $token, $matches);
+    }
+
+    if (!$ok) {
+      return null;
+    }
+
+    $function = trim($matches[1]);
+
+    if (!$this->canEvaluateFunction($function)) {
+      return null;
+    }
+
+    return array(
+      'name' => $function,
+      'argv' => array(trim($matches[2])),
+    );
+  }
+
+
+  /**
+   * @task functions
+   */
+  public function renderFunctionTokens($function, array $argv_list) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+
 }
diff --git a/src/applications/typeahead/datasource/PhabricatorTypeaheadUserParameterizedDatasource.php b/src/applications/typeahead/datasource/PhabricatorTypeaheadUserParameterizedDatasource.php
new file mode 100644
--- /dev/null
+++ b/src/applications/typeahead/datasource/PhabricatorTypeaheadUserParameterizedDatasource.php
@@ -0,0 +1,20 @@
+<?php
+
+final class PhabricatorTypeaheadUserParameterizedDatasource
+  extends PhabricatorTypeaheadCompositeDatasource {
+
+  public function getPlaceholderText() {
+    return pht('Type a username or selector...');
+  }
+
+  public function getComponentDatasources() {
+    $sources = array(
+      new PhabricatorViewerDatasource(),
+      new PhabricatorPeopleDatasource(),
+      new PhabricatorProjectMembersDatasource(),
+    );
+
+    return $sources;
+  }
+
+}
diff --git a/src/applications/typeahead/exception/PhabricatorTypeaheadInvalidTokenException.php b/src/applications/typeahead/exception/PhabricatorTypeaheadInvalidTokenException.php
new file mode 100644
--- /dev/null
+++ b/src/applications/typeahead/exception/PhabricatorTypeaheadInvalidTokenException.php
@@ -0,0 +1,3 @@
+<?php
+
+final class PhabricatorTypeaheadInvalidTokenException extends Exception {}
diff --git a/src/applications/typeahead/storage/PhabricatorTypeaheadResult.php b/src/applications/typeahead/storage/PhabricatorTypeaheadResult.php
--- a/src/applications/typeahead/storage/PhabricatorTypeaheadResult.php
+++ b/src/applications/typeahead/storage/PhabricatorTypeaheadResult.php
@@ -13,6 +13,7 @@
   private $imageSprite;
   private $icon;
   private $closed;
+  private $unique;
 
   public function setIcon($icon) {
     $this->icon = $icon;
@@ -85,8 +86,21 @@
     return $this->phid;
   }
 
+  public function setUnique($unique) {
+    $this->unique = $unique;
+    return $this;
+  }
+
   public function getSortKey() {
-    return phutil_utf8_strtolower($this->getName());
+    // Put unique results (special parameter functions) ahead of other
+    // results.
+    if ($this->unique) {
+      $prefix = 'A';
+    } else {
+      $prefix = 'B';
+    }
+
+    return $prefix.phutil_utf8_strtolower($this->getName());
   }
 
   public function getWireFormat() {
@@ -102,6 +116,7 @@
       $this->getIcon(),
       $this->closed,
       $this->imageSprite ? (string)$this->imageSprite : null,
+      $this->unique ? 1 : null,
     );
     while (end($data) === null) {
       array_pop($data);
diff --git a/src/applications/typeahead/view/PhabricatorTypeaheadTokenView.php b/src/applications/typeahead/view/PhabricatorTypeaheadTokenView.php
--- a/src/applications/typeahead/view/PhabricatorTypeaheadTokenView.php
+++ b/src/applications/typeahead/view/PhabricatorTypeaheadTokenView.php
@@ -8,7 +8,9 @@
   private $inputName;
   private $value;
 
-  public static function newForTypeaheadResult(
+  const KEY_INVALID = '<invalid>';
+
+  public static function newFromTypeaheadResult(
     PhabricatorTypeaheadResult $result) {
 
     return id(new PhabricatorTypeaheadTokenView())
@@ -17,6 +19,15 @@
       ->setValue($result->getDisplayName());
   }
 
+  public static function newFromHandle(
+    PhabricatorObjectHandle $handle) {
+
+    return id(new PhabricatorTypeaheadTokenView())
+      ->setKey($handle->getPHID())
+      ->setValue($handle->getFullName())
+      ->setIcon($handle->getIcon());
+  }
+
   public function setKey($key) {
     $this->key = $key;
     return $this;
diff --git a/src/view/control/AphrontTokenizerTemplateView.php b/src/view/control/AphrontTokenizerTemplateView.php
--- a/src/view/control/AphrontTokenizerTemplateView.php
+++ b/src/view/control/AphrontTokenizerTemplateView.php
@@ -18,7 +18,7 @@
   }
 
   public function setValue(array $value) {
-    assert_instances_of($value, 'PhabricatorObjectHandle');
+    assert_instances_of($value, 'PhabricatorTypeaheadTokenView');
     $this->value = $value;
     return $this;
   }
@@ -41,15 +41,7 @@
 
     $id = $this->id;
     $name = $this->getName();
-    $values = nonempty($this->getValue(), array());
-
-    $tokens = array();
-    foreach ($values as $key => $value) {
-      $tokens[] = $this->renderToken(
-        $value->getPHID(),
-        $value->getFullName(),
-        $value->getType());
-    }
+    $tokens = nonempty($this->getValue(), array());
 
     $input = javelin_tag(
       'input',
@@ -125,12 +117,4 @@
     return $frame;
   }
 
-  private function renderToken($key, $value, $icon) {
-    return id(new PhabricatorTypeaheadTokenView())
-      ->setKey($key)
-      ->setValue($value)
-      ->setIcon($icon)
-      ->setInputName($this->getName());
-  }
-
 }
diff --git a/src/view/form/control/AphrontFormTokenizerControl.php b/src/view/form/control/AphrontFormTokenizerControl.php
--- a/src/view/form/control/AphrontFormTokenizerControl.php
+++ b/src/view/form/control/AphrontFormTokenizerControl.php
@@ -50,19 +50,52 @@
       $id = celerity_generate_unique_node_id();
     }
 
+    $datasource = $this->datasource;
+    $datasource->setViewer($this->getUser());
+
     $placeholder = null;
     if (!strlen($this->placeholder)) {
-      if ($this->datasource) {
-        $placeholder = $this->datasource->getPlaceholderText();
+      if ($datasource) {
+        $placeholder = $datasource->getPlaceholderText();
       }
     } else {
       $placeholder = $this->placeholder;
     }
 
+    $tokens = array();
+    $values = nonempty($this->getValue(), array());
+    foreach ($values as $value) {
+      if (isset($handles[$value])) {
+        $token = PhabricatorTypeaheadTokenView::newFromHandle($handles[$value]);
+      } else {
+        $token = null;
+        if ($datasource) {
+          $function = $datasource->parseFunction($value);
+          if ($function) {
+            $token_list = $datasource->renderFunctionTokens(
+              $function['name'],
+              array($function['argv']));
+            $token = head($token_list);
+          }
+        }
+
+        if (!$token) {
+          $name = pht('Invalid Function: %s', $value);
+          $token = $datasource->newInvalidToken($name);
+        }
+
+        if ($token->getKey() == PhabricatorTypeaheadTokenView::KEY_INVALID) {
+          $token->setKey($value);
+        }
+      }
+      $token->setInputName($this->getName());
+      $tokens[] = $token;
+    }
+
     $template = new AphrontTokenizerTemplateView();
     $template->setName($name);
     $template->setID($id);
-    $template->setValue($handles);
+    $template->setValue($tokens);
 
     $username = null;
     if ($this->user) {
@@ -71,8 +104,6 @@
 
     $datasource_uri = null;
     $browse_uri = null;
-
-    $datasource = $this->datasource;
     if ($datasource) {
       $datasource->setViewer($this->getUser());
 
@@ -88,8 +119,8 @@
       Javelin::initBehavior('aphront-basic-tokenizer', array(
         'id'          => $id,
         'src'         => $datasource_uri,
-        'value'       => mpull($handles, 'getFullName', 'getPHID'),
-        'icons'       => mpull($handles, 'getIcon', 'getPHID'),
+        'value'       => mpull($tokens, 'getValue', 'getKey'),
+        'icons'       => mpull($tokens, 'getIcon', 'getKey'),
         'limit'       => $this->limit,
         'username'    => $username,
         'placeholder' => $placeholder,
@@ -111,7 +142,15 @@
       }
 
       $values = nonempty($this->getValue(), array());
-      $this->handles = $viewer->loadHandles($values);
+
+      $phids = array();
+      foreach ($values as $value) {
+        if (!PhabricatorTypeaheadDatasource::isFunctionToken($value)) {
+          $phids[] = $value;
+        }
+      }
+
+      $this->handles = $viewer->loadHandles($phids);
     }
 
     return $this->handles;
diff --git a/webroot/rsrc/externals/javelin/lib/control/typeahead/normalizer/TypeaheadNormalizer.js b/webroot/rsrc/externals/javelin/lib/control/typeahead/normalizer/TypeaheadNormalizer.js
--- a/webroot/rsrc/externals/javelin/lib/control/typeahead/normalizer/TypeaheadNormalizer.js
+++ b/webroot/rsrc/externals/javelin/lib/control/typeahead/normalizer/TypeaheadNormalizer.js
@@ -14,10 +14,14 @@
      * @return string Normalized string.
      */
     normalize : function(str) {
+
+      // NOTE: We specifically normalize "(" and ")" into spaces so that
+      // we can match tokenizer functions like "members(project)".
+
       return ('' + str)
         .toLocaleLowerCase()
-        .replace(/[\.,\/#!$%\^&\*;:{}=_`~()]/g, '')
-        .replace(/[-\[\]]/g, ' ')
+        .replace(/[\.,\/#!$%\^&\*;:{}=_`~]/g, '')
+        .replace(/[-\[\]\(\)]/g, ' ')
         .replace(/ +/g, ' ')
         .replace(/^\s*|\s*$/g, '');
     }
diff --git a/webroot/rsrc/js/application/typeahead/behavior-typeahead-search.js b/webroot/rsrc/js/application/typeahead/behavior-typeahead-search.js
--- a/webroot/rsrc/js/application/typeahead/behavior-typeahead-search.js
+++ b/webroot/rsrc/js/application/typeahead/behavior-typeahead-search.js
@@ -10,6 +10,7 @@
   var input = JX.$(config.inputID);
   var frame = JX.$(config.frameID);
   var last = input.value;
+  var in_flight = {};
 
   function update() {
     if (input.value == last) {
@@ -30,9 +31,17 @@
       return;
     }
 
+    if (value in in_flight) {
+      // We've already sent a request for this query.
+      return;
+    }
+    in_flight[value] = true;
+
     JX.DOM.alterClass(frame, 'loading', true);
     new JX.Workflow(config.uri, {q: value, format: 'html'})
       .setHandler(function(r) {
+        delete in_flight[value];
+
         if (value != input.value) {
           // The user typed some more stuff while the request was in flight,
           // so ignore the response.
diff --git a/webroot/rsrc/js/core/Prefab.js b/webroot/rsrc/js/core/Prefab.js
--- a/webroot/rsrc/js/core/Prefab.js
+++ b/webroot/rsrc/js/core/Prefab.js
@@ -287,7 +287,8 @@
         icon: icon,
         closed: closed,
         type: fields[5],
-        sprite: fields[10]
+        sprite: fields[10],
+        unique: fields[11] || false
       };
     },