diff --git a/build-system/tasks/presubmit-checks.js b/build-system/tasks/presubmit-checks.js
index 4350db3a7153..29d384e149b9 100644
--- a/build-system/tasks/presubmit-checks.js
+++ b/build-system/tasks/presubmit-checks.js
@@ -29,6 +29,10 @@ var requiresReviewPrivacy =
     'being privacy sensitive. Please file an issue asking for permission' +
     ' to use if you have not yet done so.';
 
+var privateServiceFactory = 'This service should only be installed in ' +
+    'the whitelisted files. Other modules should use a public function ' +
+    'typically called serviceNameFor.';
+
 // Terms that must not appear in our source files.
 var forbiddenTerms = {
   'DO NOT SUBMIT': '',
@@ -44,11 +48,24 @@ var forbiddenTerms = {
       'validator/validator-in-browser.js',
     ]
   },
+  // Service factories that should only be installed once.
+  'installCidService': {
+    message: privateServiceFactory,
+    whitelist: [
+      'src/service/cid-impl.js',
+      'extensions/amp-analytics/0.1/amp-analytics.js',
+      'extensions/amp-analytics/0.1/test/test-amp-analytics.js',
+      'test/functional/test-cid.js',
+      'test/functional/test-url-replacements.js'
+    ],
+  },
+  // Privacy sensitive
   'cidFor': {
     message: requiresReviewPrivacy,
     whitelist: [
       'src/cid.js',
       'src/service/cid-impl.js',
+      'src/url-replacements.js',
       'test/functional/test-cid.js',
     ],
   },
@@ -78,6 +95,7 @@ var forbiddenTerms = {
       'src/cookies.js',
       'src/experiments.js',
       'test/functional/test-cookies.js',
+      'test/functional/test-url-replacements.js',
       'tools/experiments/experiments.js',
     ]
   },
@@ -85,6 +103,7 @@ var forbiddenTerms = {
   'localStorage': {
     message: requiresReviewPrivacy,
     whitelist: [
+      'extensions/amp-analytics/0.1/test/test-amp-analytics.js',
       'test/_init_tests.js',
       'src/service/cid-impl.js',
       'test/functional/test-cid.js',
diff --git a/builtins/amp-pixel.js b/builtins/amp-pixel.js
index 58edb83eb0fa..639ead8cc9a6 100644
--- a/builtins/amp-pixel.js
+++ b/builtins/amp-pixel.js
@@ -44,16 +44,17 @@ export function installPixel(win) {
 
     /** @override */
     layoutCallback() {
-      let src = this.element.getAttribute('src');
-      src = urlReplacementsFor(this.getWin()).expand(this.assertSource(src));
-      const image = new Image();
-      image.src = src;
-      image.width = 1;
-      image.height = 1;
-      // Make it take zero space
-      this.element.style.width = 0;
-      this.element.appendChild(image);
-      return Promise.resolve();
+      const src = this.element.getAttribute('src');
+      return urlReplacementsFor(this.getWin()).expand(this.assertSource(src))
+          .then(src => {
+            const image = new Image();
+            image.src = src;
+            image.width = 1;
+            image.height = 1;
+            // Make it take zero space
+            this.element.style.width = 0;
+            this.element.appendChild(image);
+          });
     }
 
     assertSource(src) {
diff --git a/extensions/amp-analytics/0.1/amp-analytics.js b/extensions/amp-analytics/0.1/amp-analytics.js
index ae60b73a60a7..03ce039cf9ef 100644
--- a/extensions/amp-analytics/0.1/amp-analytics.js
+++ b/extensions/amp-analytics/0.1/amp-analytics.js
@@ -15,6 +15,7 @@
  */
 
 import {isExperimentOn} from '../../../src/experiments';
+import {installCidService} from '../../../src/service/cid-impl';
 import {Layout} from '../../../src/layout';
 import {log} from '../../../src/log';
 import {loadPromise} from '../../../src/event-helper';
@@ -25,6 +26,9 @@ import {addListener} from './instrumentation';
 import {ANALYTICS_CONFIG} from './vendors';
 
 
+installCidService(AMP.win);
+
+
 /** @const */
 const EXPERIMENT = 'amp-analytics';
 
@@ -59,9 +63,9 @@ export class AmpAnalytics extends AMP.BaseElement {
   }
 
   /** @override */
-  buildCallback() {
+  layoutCallback() {
     if (!this.isExperimentOn_()) {
-      return;
+      return Promise.resolve();
     }
 
     /**
@@ -85,7 +89,7 @@ export class AmpAnalytics extends AMP.BaseElement {
     if (this.hasOptedOut_()) {
       // Nothing to do when the user has opted out.
       log.fine(this.getName_(), 'User has opted out. No hits will be sent.');
-      return;
+      return Promise.resolve();
     }
 
     this.generateRequests_();
@@ -93,7 +97,7 @@ export class AmpAnalytics extends AMP.BaseElement {
     if (!Array.isArray(this.config_['triggers'])) {
       log.error(this.getName_(), 'No triggers were found in the config. No ' +
           'analytics data will be sent.');
-      return;
+      return Promise.resolve();
     }
 
     // Trigger callback can be synchronous. Do the registration at the end.
@@ -107,6 +111,7 @@ export class AmpAnalytics extends AMP.BaseElement {
       addListener(this.getWin(), trigger['on'],
           this.handleEvent_.bind(this, trigger));
     }
+    return Promise.resolve();
   }
 
   /**
@@ -227,12 +232,12 @@ export class AmpAnalytics extends AMP.BaseElement {
     });
 
     // For consistentcy with amp-pixel we also expand any url replacements.
-    request = urlReplacementsFor(this.getWin()).expand(request);
-
-    // TODO(btownsend, #1061): Add support for sendBeacon.
-    if (host && request) {
-      this.sendRequest_('https://' + host + request);
-    }
+    urlReplacementsFor(this.getWin()).expand(request).then(request => {
+      // TODO(btownsend, #1061): Add support for sendBeacon.
+      if (host && request) {
+        this.sendRequest_('https://' + host + request);
+      }
+    });
   }
 
   /**
diff --git a/extensions/amp-analytics/0.1/test/test-amp-analytics.js b/extensions/amp-analytics/0.1/test/test-amp-analytics.js
index fba3ea4b01ae..9882fe13248b 100644
--- a/extensions/amp-analytics/0.1/test/test-amp-analytics.js
+++ b/extensions/amp-analytics/0.1/test/test-amp-analytics.js
@@ -16,6 +16,8 @@
 
 import {AmpAnalytics} from '../../../../build/all/v0/amp-analytics-0.1.max';
 import {adopt} from '../../../../src/runtime';
+import {markElementScheduledForTesting} from '../../../../src/service';
+import {installCidService} from '../../../../src/service/cid-impl';
 import * as sinon from 'sinon';
 
 adopt(window);
@@ -27,6 +29,7 @@ describe('amp-analytics', function() {
   let sendRequestSpy;
 
   beforeEach(() => {
+    markElementScheduledForTesting(window, 'amp-analytics');
     sandbox = sinon.sandbox.create();
     const WindowApi = function() {};
     windowApi = new WindowApi();
@@ -37,6 +40,8 @@ describe('amp-analytics', function() {
       referrer: 'https://www.google.com/'
     };
     windowApi.Object = window.Object;
+    markElementScheduledForTesting(windowApi, 'amp-analytics');
+    installCidService(windowApi);
   });
 
   afterEach(() => {
@@ -72,8 +77,9 @@ describe('amp-analytics', function() {
     });
 
     analytics.isExperimentOn_ = () => false;
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.equal(0);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.callCount).to.equal(0);
+    });
   });
 
   it('sends a basic hit', function() {
@@ -83,8 +89,10 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.withArgs('https://example.com/bar').calledOnce).to.be.true;
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.withArgs('https://example.com/bar').calledOnce)
+          .to.be.true;
+    });
   });
 
   it('does not send a hit when config is not in a script tag', function() {
@@ -101,8 +109,9 @@ describe('amp-analytics', function() {
     analytics.createdCallback();
     sendRequestSpy = sandbox.spy(analytics, 'sendRequest_');
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.equal(0);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.callCount).to.equal(0);
+    });
   });
 
   it('does not send a hit when multiple child tags exist', function() {
@@ -114,8 +123,9 @@ describe('amp-analytics', function() {
     const script2 = document.createElement('script');
     script2.setAttribute('type', 'application/json');
     analytics.element.appendChild(script2);
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.equal(0);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.callCount).to.equal(0);
+    });
   });
 
   it('does not send a hit when script tag does not have a type attribute',
@@ -134,8 +144,9 @@ describe('amp-analytics', function() {
         analytics.createdCallback();
         sendRequestSpy = sandbox.spy(analytics, 'sendRequest_');
 
-        analytics.buildCallback();
-        expect(sendRequestSpy.callCount).to.equal(0);
+        return analytics.layoutCallback().then(() => {
+          expect(sendRequestSpy.callCount).to.equal(0);
+        });
       });
 
   it('does not send a hit when host is not provided', function() {
@@ -144,8 +155,9 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.equal(0);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.callCount).to.equal(0);
+    });
   });
 
   it('does not send a hit when request is not provided', function() {
@@ -155,8 +167,9 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.equal(0);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.callCount).to.equal(0);
+    });
   });
 
   it('does not send a hit when request type is not defined', function() {
@@ -165,8 +178,9 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.equal(0);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.callCount).to.equal(0);
+    });
   });
 
   it('expands nested requests', function() {
@@ -176,10 +190,11 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0])
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0])
         .to.equal('https://example.com/bar&f1&baz');
+    });
   });
 
   it('expands nested requests', function() {
@@ -189,9 +204,10 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal('https://example.com/bar&b1');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal('https://example.com/bar&b1');
+    });
   });
 
   it('expands recursive requests', function() {
@@ -201,10 +217,11 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0])
-        .to.equal('https://example.com/bar&/bar&/bar&&baz&baz&baz');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0])
+          .to.equal('https://example.com/bar&/bar&/bar&&baz&baz&baz');
+    });
   });
 
   it('fills in the platform variables', function() {
@@ -214,9 +231,34 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.not.match(/AMPDOC_URL/);
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.not.match(/AMPDOC_URL/);
+    });
+  });
+
+  it('fills cid for proxy host', function() {
+    windowApi.localStorage = {
+      getItem: function(name) {
+        return JSON.stringify({
+          time: new Date().getTime(),
+          cid: 'base'
+        });
+      },
+    };
+    windowApi.location.href = '/c/www.test.com/abc';
+    const analytics = getAnalyticsTag({
+      'host': 'example.com',
+      'requests': {'foo': 'cid=CLIENT_ID(analytics-abc)'},
+      'triggers': [{'on': 'visible', 'request': 'foo'}]
+    });
+
+    analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+         'https://example.comcid=uQVAtQyO978OPCNBZXWOKRDcxSORw9GQfB' +
+          'x2CyJSF0MnkIPeeX9ruacSFPgQ0HSD');
+    });
   });
 
   it('merges host correctly', function() {
@@ -230,9 +272,10 @@ describe('amp-analytics', function() {
         'host': 'example.com'
       }
     };
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal('https://example.com/bar');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal('https://example.com/bar');
+    });
   });
 
   it('merges requests correctly', function() {
@@ -247,9 +290,10 @@ describe('amp-analytics', function() {
         'requests': {'foo': '/bar', 'bar': 'foobar'}
       }
     };
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal('https://example.com/foobar');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal('https://example.com/foobar');
+    });
   });
 
   it('merges objects correctly', function() {
@@ -259,33 +303,34 @@ describe('amp-analytics', function() {
       'triggers': [{'on': 'visible', 'request': 'foo'}]
     });
 
-    analytics.buildCallback();
-    expect(analytics.mergeObjects_({}, {})).to.deep.equal({});
-    expect(analytics.mergeObjects_({'foo': 1}, {'1': 1}))
-        .to.deep.equal({'foo': 1, '1': 1});
-    expect(analytics.mergeObjects_({'1': 1}, {'bar': 'bar'}))
-        .to.deep.equal({'1': 1, 'bar': 'bar'});
-    expect(analytics.mergeObjects_(
-        {'foo': [1, 2, 3, 4]},
-        {'bar': [4, 5, 6, 7]}))
-        .to.deep.equal(
-            {'foo': [1,2, 3, 4], 'bar': [4, 5, 6, 7]});
-    expect(analytics.mergeObjects_(
-        null,
-        {'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}}))
-        .to.deep.equal({'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}});
-    expect(analytics.mergeObjects_(
-        undefined,
-        {'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}}))
-        .to.deep.equal({'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}});
-    expect(analytics.mergeObjects_(
-        {'baz': 'bar', 'foobar': {'foobar': ['abc', 'def']}},
-        {'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}}))
-        .to.deep.equal({
-          'foo': 'bar',
-          'baz': 'bar',
-          'foobar': {'foobar': ['abc', 'def']}
-        });
+    return analytics.layoutCallback().then(() => {
+      expect(analytics.mergeObjects_({}, {})).to.deep.equal({});
+      expect(analytics.mergeObjects_({'foo': 1}, {'1': 1}))
+          .to.deep.equal({'foo': 1, '1': 1});
+      expect(analytics.mergeObjects_({'1': 1}, {'bar': 'bar'}))
+          .to.deep.equal({'1': 1, 'bar': 'bar'});
+      expect(analytics.mergeObjects_(
+          {'foo': [1, 2, 3, 4]},
+          {'bar': [4, 5, 6, 7]}))
+          .to.deep.equal(
+              {'foo': [1,2, 3, 4], 'bar': [4, 5, 6, 7]});
+      expect(analytics.mergeObjects_(
+          null,
+          {'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}}))
+          .to.deep.equal({'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}});
+      expect(analytics.mergeObjects_(
+          undefined,
+          {'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}}))
+          .to.deep.equal({'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}});
+      expect(analytics.mergeObjects_(
+          {'baz': 'bar', 'foobar': {'foobar': ['abc', 'def']}},
+          {'foo': 'bar', 'baz': {'foobar': ['abc', 'def']}}))
+          .to.deep.equal({
+            'foo': 'bar',
+            'baz': 'bar',
+            'foobar': {'foobar': ['abc', 'def']}
+          });
+    });
   });
 
   it('expands trigger vars', () => {
@@ -300,10 +345,11 @@ describe('amp-analytics', function() {
           'var2': 'test2'
         }
       }]});
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal(
-        'https://example.com/test1=x&test2=test2');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+          'https://example.com/test1=x&test2=test2');
+    });
   });
 
   it('expands config vars', () => {
@@ -315,10 +361,11 @@ describe('amp-analytics', function() {
       },
       'requests': {'pageview': '/test1=${var1}&test2=${var2}'},
       'triggers': [{'on': 'visible', 'request': 'pageview'}]});
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal(
-        'https://example.com/test1=x&test2=test2');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+          'https://example.com/test1=x&test2=test2');
+    });
   });
 
   it('expands trigger vars with higher precedence than config vars', () => {
@@ -335,10 +382,11 @@ describe('amp-analytics', function() {
         'vars': {
           'var1': 'trigger1'
         }}]});
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal(
-        'https://example.com/test1=trigger1&test2=config2');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+          'https://example.com/test1=trigger1&test2=config2');
+    });
   });
 
   it('does not expand nested vars', () => {
@@ -352,10 +400,11 @@ describe('amp-analytics', function() {
           'var1': '${var2}',
           'var2': 't2'
         }}]});
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal(
-        'https://example.com/test=%24%7Bvar2%7D');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+          'https://example.com/test=%24%7Bvar2%7D');
+    });
   });
 
   it('expands and encodes requests, config vars, and trigger vars', () => {
@@ -376,11 +425,12 @@ describe('amp-analytics', function() {
           't1': 'trigger=1',
           't2': 'trigger?2'
         }}]});
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal(
-        'https://example.com/test?c1=config%201&t1=trigger%3D1&' +
-        'c2=config%262&t2=trigger%3F2');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+          'https://example.com/test?c1=config%201&t1=trigger%3D1&' +
+          'c2=config%262&t2=trigger%3F2');
+    });
   });
 
   it('expands url-replacements vars', () => {
@@ -395,11 +445,12 @@ describe('amp-analytics', function() {
           'var2': 'DOCUMENT_REFERRER'
         }
       }]});
-    analytics.buildCallback();
-    expect(sendRequestSpy.calledOnce).to.be.true;
-    expect(sendRequestSpy.args[0][0]).to.equal(
-        'https://example.com/test1=x&test2=https%3A%2F%2Fwww.google.com%2F' +
-        '&title=Test%20Title');
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.calledOnce).to.be.true;
+      expect(sendRequestSpy.args[0][0]).to.equal(
+          'https://example.com/test1=x&test2=https%3A%2F%2Fwww.google.com%2F' +
+          '&title=Test%20Title');
+    });
   });
 
   it('respects optout', function() {
@@ -410,21 +461,22 @@ describe('amp-analytics', function() {
       'optout': 'foo.bar'
     };
     let analytics = getAnalyticsTag(config);
-    analytics.buildCallback();
-    expect(sendRequestSpy.withArgs('https://example.com/bar').calledOnce)
-        .to.be.true;
-
-    sendRequestSpy.reset();
-    windowApi['foo'] = {'bar': function() { return true; }};
-    analytics = getAnalyticsTag(config);
-    analytics.buildCallback();
-    expect(sendRequestSpy.callCount).to.be.equal(0);
-
-    sendRequestSpy.reset();
-    windowApi['foo'] = {'bar': function() { return false; }};
-    analytics = getAnalyticsTag(config);
-    analytics.buildCallback();
-    expect(sendRequestSpy.withArgs('https://example.com/bar').calledOnce)
-        .to.be.true;
+    return analytics.layoutCallback().then(() => {
+      expect(sendRequestSpy.withArgs('https://example.com/bar').calledOnce)
+          .to.be.true;
+      sendRequestSpy.reset();
+      windowApi['foo'] = {'bar': function() { return true; }};
+      analytics = getAnalyticsTag(config);
+      analytics.layoutCallback().then(() => {
+        expect(sendRequestSpy.callCount).to.be.equal(0);
+        sendRequestSpy.reset();
+        windowApi['foo'] = {'bar': function() { return false; }};
+        analytics = getAnalyticsTag(config);
+        analytics.layoutCallback().then(() => {
+          expect(sendRequestSpy.withArgs('https://example.com/bar').calledOnce)
+              .to.be.true;
+        });
+      });
+    });
   });
 });
diff --git a/extensions/amp-list/0.1/amp-list.js b/extensions/amp-list/0.1/amp-list.js
index a3cf689fe64e..09d7d2956826 100644
--- a/extensions/amp-list/0.1/amp-list.js
+++ b/extensions/amp-list/0.1/amp-list.js
@@ -56,19 +56,20 @@ export class AmpList extends AMP.BaseElement {
 
   /** @override */
   layoutCallback() {
-    const src = this.urlReplacements_.expand(assertHttpsUrl(
-        this.element.getAttribute('src'), this.element));
-    const opts = {
-      credentials: this.element.getAttribute('credentials')
-    };
-    return xhrFor(this.getWin()).fetchJson(src, opts).then(data => {
-      assert(typeof data == 'object' && Array.isArray(data['items']),
-          'Response must be {items: []} object %s %s',
-          this.element, data);
-      const items = data['items'];
-      return templatesFor(this.getWin()).findAndRenderTemplateArray(
-          this.element, items).then(this.rendered_.bind(this));
-    });
+    return this.urlReplacements_.expand(assertHttpsUrl(
+        this.element.getAttribute('src'), this.element)).then(src => {
+          const opts = {
+            credentials: this.element.getAttribute('credentials')
+          };
+          return xhrFor(this.getWin()).fetchJson(src, opts);
+        }).then(data => {
+          assert(typeof data == 'object' && Array.isArray(data['items']),
+              'Response must be {items: []} object %s %s',
+              this.element, data);
+          const items = data['items'];
+          return templatesFor(this.getWin()).findAndRenderTemplateArray(
+              this.element, items).then(this.rendered_.bind(this));
+        });
   }
 
   /**
diff --git a/src/runtime.js b/src/runtime.js
index db0c71f53b0a..00e7ad679f0c 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -47,7 +47,9 @@ export function adopt(global) {
   // of functions
   const preregisteredElements = global.AMP || [];
 
-  global.AMP = {};
+  global.AMP = {
+    win: global
+  };
 
   /**
    * Registers an extended element and installs its styles.
diff --git a/src/service.js b/src/service.js
index 5afaaec7e9f3..209d358f72f0 100644
--- a/src/service.js
+++ b/src/service.js
@@ -75,8 +75,9 @@ export function getService(win, id, opt_factory) {
 export function getElementService(win, id, providedByElement) {
   assert(isElementScheduled(win, providedByElement),
       'Service %s was requested to be provided through %s, ' +
-      'but %s is not loaded in the current page.',
-      id, providedByElement, providedByElement);
+      'but %s is not loaded in the current page. To fix this ' +
+      'problem load the JavaScript file for %s in this page.',
+      id, providedByElement, providedByElement, providedByElement);
   const services = getServices(win, id);
   const s = services[id];
   if (s) {
@@ -115,6 +116,20 @@ function isElementScheduled(win, elementName) {
   return !!win.ampExtendedElements[elementName];
 }
 
+/**
+ * In order to provide better error messages we only allow to retrieve
+ * services from other elements if those elements are loaded in the page.
+ * This makes it possible to mark an element as loaded in a test.
+ * @param {!Window} win
+ * @param {string} elementName Name of an extended custom element.
+ */
+export function markElementScheduledForTesting(win, elementName) {
+  if (!win.ampExtendedElements) {
+    win.ampExtendedElements = {};
+  }
+  win.ampExtendedElements[elementName] = true;
+}
+
 /**
  * Returns the object that holds the services registered in a window.
  * @param {!Window} win
diff --git a/src/service/cid-impl.js b/src/service/cid-impl.js
index 0af3430c6d5d..028724d10b7d 100644
--- a/src/service/cid-impl.js
+++ b/src/service/cid-impl.js
@@ -84,6 +84,9 @@ class Cid {
    *      given.
    */
   get(externalCidScope, consent, opt_persistenceConsent) {
+    assert(/^[a-zA-Z0-9-_]+$/.test(externalCidScope),
+        'The client id name must match only use the characters ' +
+        '[a-zA-Z0-9-_]+\nInstead found %s', externalCidScope);
     return consent.then(() => {
       return getExternalCid(this, externalCidScope,
           opt_persistenceConsent || consent);
diff --git a/src/url-replacements.js b/src/url-replacements.js
index 70b179c15b48..48f47721890a 100644
--- a/src/url-replacements.js
+++ b/src/url-replacements.js
@@ -15,8 +15,9 @@
  */
 
 import {assert} from './asserts';
+import {cidFor} from './cid';
 import {documentInfoFor} from './document-info';
-import {getService} from './service';
+import {getService, getElementService} from './service';
 import {parseUrl, removeFragment} from './url';
 
 
@@ -82,7 +83,16 @@ class UrlReplacements {
     // single page view. It should have sufficient entropy to be unique for
     // all the page views a single user is making at a time.
     this.set_('PAGE_VIEW_ID', () => {
-      documentInfoFor(this.win_).pageViewId;
+      return documentInfoFor(this.win_).pageViewId;
+    });
+
+    this.set_('CLIENT_ID', (data, name) => {
+      return cidFor(this.win_).then(cid => {
+        return cid.get(name,
+            // TODO(@cramforce): Hook up mechanism to get consent to id
+            // generation.
+            Promise.resolve());
+      });
     });
   }
 
@@ -95,8 +105,6 @@ class UrlReplacements {
    * @private
    */
   set_(varName, resolver) {
-    assert(varName == varName.toUpperCase(),
-        'Variable name must be in upper case: %s', varName);
     this.replacements_[varName] = resolver;
     this.replacementExpr_ = undefined;
     return this;
@@ -107,19 +115,42 @@ class UrlReplacements {
    * resolved values.
    * @param {string} url
    * @param {*} opt_data
-   * @return {string}
+   * @return {!Promise<string>}
    */
   expand(url, opt_data) {
     const expr = this.getExpr_();
-    return url.replace(expr, (match, name) => {
-      let val = this.replacements_[name](opt_data);
+    let replacementPromise;
+    const encodeValue = val => {
       // Value 0 is specialcased because the numeric 0 is a valid substitution
       // value.
       if (!val && val !== 0) {
         val = '';
       }
       return encodeURIComponent(val);
+    };
+    url = url.replace(expr, (match, name, arg) => {
+      const val = this.replacements_[name](opt_data, arg);
+      // In case the produced value is a promise, we don't actually
+      // replace anything here, but do it again when the promise resolves.
+      if (val && val.then) {
+        const p = val.then(v => {
+          url = url.replace(match, encodeValue(v));
+        });
+        if (replacementPromise) {
+          replacementPromise = replacementPromise.then(() => p);
+        } else {
+          replacementPromise = p;
+        }
+        return match;
+      }
+      return encodeValue(val);
     });
+
+    if (replacementPromise) {
+      replacementPromise = replacementPromise.then(() => url);
+    }
+
+    return replacementPromise || Promise.resolve(url);
   }
 
   /**
@@ -132,7 +163,13 @@ class UrlReplacements {
       for (const k in this.replacements_) {
         all += (all.length > 0 ? '|' : '') + k;
       }
-      this.replacementExpr_ = new RegExp('\\$?(' + all + ')', 'g');
+      this.replacementExpr_ =
+          // Match the given replacement patterns, as well as optionally
+          // arguments to the replacement behind it in parantheses.
+          // Example string that match
+          // FOO_BAR
+          // FOO_BAR(arg1)
+          new RegExp('\\$?(' + all + ')(?:\\(([a-zA-Z-_]+)\\))?', 'g');
     }
     return this.replacementExpr_;
   }
diff --git a/test/_init_tests.js b/test/_init_tests.js
index 4d997e187df7..f75f36a88d2b 100644
--- a/test/_init_tests.js
+++ b/test/_init_tests.js
@@ -61,6 +61,7 @@ afterEach(() => {
     }
   }
   window.localStorage.clear();
+  window.ampExtendedElements = {};
 });
 
 chai.Assertion.addMethod('attribute', function(attr) {
diff --git a/test/functional/test-cid.js b/test/functional/test-cid.js
index 5a2da23b94bd..211d1395a439 100644
--- a/test/functional/test-cid.js
+++ b/test/functional/test-cid.js
@@ -235,7 +235,7 @@ describe('cid', () => {
     const consent = timer.promise(100).then(() => {
       nonce = 'timer fired';
     });
-    const p = cid.get('', consent).then(c => {
+    const p = cid.get('test', consent).then(c => {
       expect(nonce).to.equal('timer fired');
     });
     clock.tick(100);
@@ -246,6 +246,12 @@ describe('cid', () => {
     return expect(cid.get('abc', Promise.reject())).to.be.rejected;
   });
 
+  it('should fail on invalid scope', () => {
+    expect(() => {
+      cid.get('$$$', Promise.resolve());
+    }).to.throw(/\$\$\$/);
+  });
+
   it('should not store until persistence promise resolves', () => {
     let resolve;
     const persistencePromise = new Promise(r => {
diff --git a/test/functional/test-url-replacements.js b/test/functional/test-url-replacements.js
index b135c6a6c629..16de22a10a4e 100644
--- a/test/functional/test-url-replacements.js
+++ b/test/functional/test-url-replacements.js
@@ -16,17 +16,25 @@
 
 import {createIframePromise} from '../../testing/iframe';
 import {urlReplacementsFor} from '../../src/url-replacements';
+import {markElementScheduledForTesting} from '../../src/service';
+import {installCidService} from '../../src/service/cid-impl';
+import {setCookie} from '../../src/cookies';
 
 
 describe('UrlReplacements', () => {
 
-  function expand(url) {
+  function expand(url, withCid) {
     return createIframePromise().then(iframe => {
       iframe.doc.title = 'Pixel Test';
       const link = iframe.doc.createElement('link');
       link.setAttribute('href', 'https://pinterest.com/pin1');
       link.setAttribute('rel', 'canonical');
       iframe.doc.head.appendChild(link);
+      if (withCid) {
+        markElementScheduledForTesting(iframe.win, 'amp-analytics');
+        installCidService(iframe.win);
+      }
+
       const replacements = urlReplacementsFor(iframe.win);
       return replacements.expand(url);
     });
@@ -82,10 +90,19 @@ describe('UrlReplacements', () => {
 
   it('should replace PAGE_VIEW_ID', () => {
     return expand('?pid=PAGE_VIEW_ID').then(res => {
-      expect(res).to.not.match(/pid=\d+/);
+      expect(res).to.match(/pid=\d+/);
     });
   });
 
+  it('should replace CLIENT_ID', () => {
+    setCookie(window, 'url-abc', 'cid-for-abc');
+    setCookie(window, 'url-xyz', 'cid-for-xyz');
+    return expand('?a=CLIENT_ID(url-abc)&b=CLIENT_ID(url-xyz)', true)
+        .then(res => {
+          expect(res).to.equal('?a=cid-for-abc&b=cid-for-xyz');
+        });
+  });
+
   it('should accept $expressions', () => {
     return expand('?href=$CANONICAL_URL').then(res => {
       expect(res).to.equal('?href=https%3A%2F%2Fpinterest.com%2Fpin1');
@@ -109,12 +126,26 @@ describe('UrlReplacements', () => {
   it('should replace new substitutions', () => {
     const replacements = urlReplacementsFor(window);
     replacements.set_('ONE', () => 'a');
-    expect(replacements.expand('?a=ONE')).to.equal('?a=a');
-
+    expect(replacements.expand('?a=ONE')).to.eventually.equal('?a=a');
     replacements.set_('ONE', () => 'b');
-    expect(replacements.expand('?a=ONE')).to.equal('?a=b');
-
     replacements.set_('TWO', () => 'b');
-    expect(replacements.expand('?b=TWO')).to.equal('?b=b');
+    return expect(replacements.expand('?a=ONE&b=TWO'))
+        .to.eventually.equal('?a=b&b=b');
+  });
+
+  it('should support positional arguments', () => {
+    const replacements = urlReplacementsFor(window);
+    replacements.set_('FN', (data, one) => one);
+    expect(replacements.expand('?a=FN(xyz)')).to.eventually.equal('?a=xyz');
+  });
+
+  it('should support promises as replacements', () => {
+    const replacements = urlReplacementsFor(window);
+    replacements.set_('P1', () => Promise.resolve('abc '));
+    replacements.set_('P2', () => Promise.resolve('xyz'));
+    replacements.set_('P3', () => Promise.resolve('123'));
+    replacements.set_('OTHER', () => 'foo');
+    return expect(replacements.expand('?a=P1&b=P2&c=P3&d=OTHER'))
+        .to.eventually.equal('?a=abc%20&b=xyz&c=123&d=foo');
   });
 });