diff --git a/java/com/google/gerrit/entities/PermissionRule.java b/java/com/google/gerrit/entities/PermissionRule.java
index 9a2d31e..1665c1c 100644
--- a/java/com/google/gerrit/entities/PermissionRule.java
+++ b/java/com/google/gerrit/entities/PermissionRule.java
@@ -202,6 +202,9 @@
         int dotdot = range.indexOf("..");
         int min = parseInt(range.substring(0, dotdot));
         int max = parseInt(range.substring(dotdot + 2));
+        if (min > max) {
+          throw new IllegalArgumentException("Invalid range in rule: " + orig);
+        }
         rule.setRange(min, max);
       } else {
         throw new IllegalArgumentException("Invalid range in rule: " + orig);
diff --git a/java/com/google/gerrit/server/restapi/project/SetAccess.java b/java/com/google/gerrit/server/restapi/project/SetAccess.java
index 23d60fe..6957275 100644
--- a/java/com/google/gerrit/server/restapi/project/SetAccess.java
+++ b/java/com/google/gerrit/server/restapi/project/SetAccess.java
@@ -19,6 +19,9 @@
 import com.google.gerrit.entities.AccessSection;
 import com.google.gerrit.entities.Project;
 import com.google.gerrit.exceptions.InvalidNameException;
+import com.google.gerrit.extensions.api.access.AccessSectionInfo;
+import com.google.gerrit.extensions.api.access.PermissionInfo;
+import com.google.gerrit.extensions.api.access.PermissionRuleInfo;
 import com.google.gerrit.extensions.api.access.ProjectAccessInfo;
 import com.google.gerrit.extensions.api.access.ProjectAccessInput;
 import com.google.gerrit.extensions.restapi.BadRequestException;
@@ -39,6 +42,7 @@
 import com.google.inject.Provider;
 import com.google.inject.Singleton;
 import java.util.List;
+import java.util.Map;
 import org.eclipse.jgit.errors.ConfigInvalidException;
 
 @Singleton
@@ -80,6 +84,8 @@
       throws Exception {
     MetaDataUpdate.User metaDataUpdateUser = metaDataUpdateFactory.get();
 
+    validateInput(input);
+
     ProjectConfig config;
 
     List<AccessSection> removals =
@@ -137,4 +143,65 @@
 
     return Response.ok(getAccess.apply(rsrc.getNameKey()));
   }
+
+  private static void validateInput(ProjectAccessInput input) throws BadRequestException {
+    if (input.add != null) {
+      for (Map.Entry<String, AccessSectionInfo> accessSectionEntry : input.add.entrySet()) {
+        validateAccessSection(accessSectionEntry.getKey(), accessSectionEntry.getValue());
+      }
+    }
+  }
+
+  private static void validateAccessSection(String ref, AccessSectionInfo accessSectionInfo)
+      throws BadRequestException {
+    if (accessSectionInfo != null) {
+      for (Map.Entry<String, PermissionInfo> permissionEntry :
+          accessSectionInfo.permissions.entrySet()) {
+        validatePermission(ref, permissionEntry.getKey(), permissionEntry.getValue());
+      }
+    }
+  }
+
+  private static void validatePermission(
+      String ref, String permission, PermissionInfo permissionInfo) throws BadRequestException {
+    if (permissionInfo != null) {
+      for (Map.Entry<String, PermissionRuleInfo> permissionRuleEntry :
+          permissionInfo.rules.entrySet()) {
+        validatePermissionRule(
+            ref, permission, permissionRuleEntry.getKey(), permissionRuleEntry.getValue());
+      }
+    }
+  }
+
+  private static void validatePermissionRule(
+      String ref, String permission, String groupId, PermissionRuleInfo permissionRuleInfo)
+      throws BadRequestException {
+    if (permissionRuleInfo != null) {
+      if (permissionRuleInfo.min != null || permissionRuleInfo.max != null) {
+        if (permissionRuleInfo.min == null) {
+          throw new BadRequestException(
+              String.format(
+                  "Invalid range for permission rule that assigns %s to group %s on ref %s:"
+                      + " ..%d (min is required if max is set)",
+                  permission, groupId, ref, permissionRuleInfo.max));
+        }
+
+        if (permissionRuleInfo.max == null) {
+          throw new BadRequestException(
+              String.format(
+                  "Invalid range for permission rule that assigns %s to group %s on ref %s:"
+                      + " %d.. (max is required if min is set)",
+                  permission, groupId, ref, permissionRuleInfo.min));
+        }
+
+        if (permissionRuleInfo.min > permissionRuleInfo.max) {
+          throw new BadRequestException(
+              String.format(
+                  "Invalid range for permission rule that assigns %s to group %s on ref %s:"
+                      + " %d..%d (min must be <= max)",
+                  permission, groupId, ref, permissionRuleInfo.min, permissionRuleInfo.max));
+        }
+      }
+    }
+  }
 }
diff --git a/javatests/com/google/gerrit/acceptance/api/project/AccessIT.java b/javatests/com/google/gerrit/acceptance/api/project/AccessIT.java
index 630958c..6bd2b68 100644
--- a/javatests/com/google/gerrit/acceptance/api/project/AccessIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/project/AccessIT.java
@@ -359,6 +359,79 @@
   }
 
   @Test
+  public void addAccessSectionWithInvalidLabelRange_minGreaterThanMax() throws Exception {
+    ProjectAccessInput accessInput = newProjectAccessInput();
+    AccessSectionInfo accessSectionInfo = createDefaultAccessSectionInfo();
+
+    PermissionInfo permissionInfo = newPermissionInfo();
+    PermissionRuleInfo permissionRuleInfo =
+        new PermissionRuleInfo(PermissionRuleInfo.Action.ALLOW, false);
+    permissionInfo.rules.put(SystemGroupBackend.REGISTERED_USERS.get(), permissionRuleInfo);
+    permissionRuleInfo.min = 1;
+    permissionRuleInfo.max = -1;
+    accessSectionInfo.permissions.put("label-Code-Review", permissionInfo);
+
+    accessInput.add.put(REFS_HEADS, accessSectionInfo);
+    BadRequestException ex =
+        assertThrows(BadRequestException.class, () -> pApi().access(accessInput));
+    assertThat(ex)
+        .hasMessageThat()
+        .isEqualTo(
+            String.format(
+                "Invalid range for permission rule that assigns label-Code-Review to group %s"
+                    + " on ref refs/heads/*: 1..-1 (min must be <= max)",
+                SystemGroupBackend.REGISTERED_USERS.get()));
+  }
+
+  @Test
+  public void addAccessSectionWithInvalidLabelRange_minSetMaxMissing() throws Exception {
+    ProjectAccessInput accessInput = newProjectAccessInput();
+    AccessSectionInfo accessSectionInfo = createDefaultAccessSectionInfo();
+
+    PermissionInfo permissionInfo = newPermissionInfo();
+    PermissionRuleInfo permissionRuleInfo =
+        new PermissionRuleInfo(PermissionRuleInfo.Action.ALLOW, false);
+    permissionInfo.rules.put(SystemGroupBackend.REGISTERED_USERS.get(), permissionRuleInfo);
+    permissionRuleInfo.min = -1;
+    accessSectionInfo.permissions.put("label-Code-Review", permissionInfo);
+
+    accessInput.add.put(REFS_HEADS, accessSectionInfo);
+    BadRequestException ex =
+        assertThrows(BadRequestException.class, () -> pApi().access(accessInput));
+    assertThat(ex)
+        .hasMessageThat()
+        .isEqualTo(
+            String.format(
+                "Invalid range for permission rule that assigns label-Code-Review to group %s"
+                    + " on ref refs/heads/*: -1.. (max is required if min is set)",
+                SystemGroupBackend.REGISTERED_USERS.get()));
+  }
+
+  @Test
+  public void addAccessSectionWithInvalidLabelRange_maxSetMinMissing() throws Exception {
+    ProjectAccessInput accessInput = newProjectAccessInput();
+    AccessSectionInfo accessSectionInfo = createDefaultAccessSectionInfo();
+
+    PermissionInfo permissionInfo = newPermissionInfo();
+    PermissionRuleInfo permissionRuleInfo =
+        new PermissionRuleInfo(PermissionRuleInfo.Action.ALLOW, false);
+    permissionInfo.rules.put(SystemGroupBackend.REGISTERED_USERS.get(), permissionRuleInfo);
+    permissionRuleInfo.max = 1;
+    accessSectionInfo.permissions.put("label-Code-Review", permissionInfo);
+
+    accessInput.add.put(REFS_HEADS, accessSectionInfo);
+    BadRequestException ex =
+        assertThrows(BadRequestException.class, () -> pApi().access(accessInput));
+    assertThat(ex)
+        .hasMessageThat()
+        .isEqualTo(
+            String.format(
+                "Invalid range for permission rule that assigns label-Code-Review to group %s"
+                    + " on ref refs/heads/*: ..1 (min is required if max is set)",
+                SystemGroupBackend.REGISTERED_USERS.get()));
+  }
+
+  @Test
   public void createAccessChangeNop() throws Exception {
     ProjectAccessInput accessInput = newProjectAccessInput();
     assertThrows(BadRequestException.class, () -> pApi().accessChange(accessInput));
diff --git a/javatests/com/google/gerrit/acceptance/api/project/ProjectConfigIT.java b/javatests/com/google/gerrit/acceptance/api/project/ProjectConfigIT.java
index 5fd2159..28a0196 100644
--- a/javatests/com/google/gerrit/acceptance/api/project/ProjectConfigIT.java
+++ b/javatests/com/google/gerrit/acceptance/api/project/ProjectConfigIT.java
@@ -18,6 +18,7 @@
 import static com.google.gerrit.acceptance.GitUtil.fetch;
 
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableMap;
 import com.google.gerrit.acceptance.AbstractDaemonTest;
 import com.google.gerrit.acceptance.PushOneCommit;
 import com.google.gerrit.acceptance.testsuite.project.ProjectOperations;
@@ -32,6 +33,8 @@
 import com.google.gerrit.extensions.common.ChangeInfo;
 import com.google.gerrit.extensions.common.ChangeInput;
 import com.google.gerrit.git.ObjectIds;
+import com.google.gerrit.server.group.SystemGroupBackend;
+import com.google.gerrit.server.project.GroupList;
 import com.google.gerrit.server.project.LabelConfigValidator;
 import com.google.gerrit.server.project.ProjectConfig;
 import com.google.inject.Inject;
@@ -155,6 +158,81 @@
   }
 
   @Test
+  public void rejectCreatingLabelPermissionWithInvalidRange_minGreaterThanMax() throws Exception {
+    fetchRefsMetaConfig();
+    PushOneCommit push =
+        pushFactory.create(
+            admin.newIdent(),
+            testRepo,
+            "Test Change",
+            ImmutableMap.of(
+                ProjectConfig.PROJECT_CONFIG,
+                "[access \"refs/heads/*\"]\n  label-Code-Review = 1..-1 group Registered-Users",
+                GroupList.FILE_NAME,
+                String.format("%s\tRegistered-Users", SystemGroupBackend.REGISTERED_USERS.get())));
+    PushOneCommit.Result r = push.to(RefNames.REFS_CONFIG);
+    r.assertErrorStatus(
+        String.format("commit %s: invalid project configuration", abbreviateName(r.getCommit())));
+    r.assertMessage(
+        String.format(
+            "ERROR: commit %s: invalid project configuration:\n"
+                + "ERROR: commit %s:   project.config: invalid rule in"
+                + " access.refs/heads/*.label-Code-Review:"
+                + " invalid range in rule: 1..-1 group Registered-Users",
+            abbreviateName(r.getCommit()), abbreviateName(r.getCommit())));
+  }
+
+  @Test
+  public void rejectCreatingLabelPermissionWithInvalidRange_minSetMaxMissing() throws Exception {
+    fetchRefsMetaConfig();
+    PushOneCommit push =
+        pushFactory.create(
+            admin.newIdent(),
+            testRepo,
+            "Test Change",
+            ImmutableMap.of(
+                ProjectConfig.PROJECT_CONFIG,
+                "[access \"refs/heads/*\"]\n  label-Code-Review = -1.. group Registered-Users",
+                GroupList.FILE_NAME,
+                String.format("%s\tRegistered-Users", SystemGroupBackend.REGISTERED_USERS.get())));
+    PushOneCommit.Result r = push.to(RefNames.REFS_CONFIG);
+    r.assertErrorStatus(
+        String.format("commit %s: invalid project configuration", abbreviateName(r.getCommit())));
+    r.assertMessage(
+        String.format(
+            "ERROR: commit %s: invalid project configuration:\n"
+                + "ERROR: commit %s:   project.config: invalid rule in"
+                + " access.refs/heads/*.label-Code-Review:"
+                + " invalid range in rule: -1.. group Registered-Users",
+            abbreviateName(r.getCommit()), abbreviateName(r.getCommit())));
+  }
+
+  @Test
+  public void rejectCreatingLabelPermissionWithInvalidRange_maxSetMinMissing() throws Exception {
+    fetchRefsMetaConfig();
+    PushOneCommit push =
+        pushFactory.create(
+            admin.newIdent(),
+            testRepo,
+            "Test Change",
+            ImmutableMap.of(
+                ProjectConfig.PROJECT_CONFIG,
+                "[access \"refs/heads/*\"]\n  label-Code-Review = ..1 group Registered-Users",
+                GroupList.FILE_NAME,
+                String.format("%s\tRegistered-Users", SystemGroupBackend.REGISTERED_USERS.get())));
+    PushOneCommit.Result r = push.to(RefNames.REFS_CONFIG);
+    r.assertErrorStatus(
+        String.format("commit %s: invalid project configuration", abbreviateName(r.getCommit())));
+    r.assertMessage(
+        String.format(
+            "ERROR: commit %s: invalid project configuration:\n"
+                + "ERROR: commit %s:   project.config: invalid rule in"
+                + " access.refs/heads/*.label-Code-Review:"
+                + " invalid range in rule: ..1 group Registered-Users",
+            abbreviateName(r.getCommit()), abbreviateName(r.getCommit())));
+  }
+
+  @Test
   public void rejectSettingCopyMinScore() throws Exception {
     testRejectSettingLabelFlag(
         LabelConfigValidator.KEY_COPY_MIN_SCORE, /* value= */ true, "is:MIN");
diff --git a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts
index af4e87e..1be5fa3 100644
--- a/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts
+++ b/polygerrit-ui/app/elements/admin/gr-admin-view/gr-admin-view.ts
@@ -129,6 +129,7 @@
 
   constructor() {
     super();
+    this.addEventListener('reload', () => window.location.reload());
     subscribe(
       this,
       () => this.getAdminViewModel().state$,
diff --git a/polygerrit-ui/app/elements/admin/gr-create-pointer-dialog/gr-create-pointer-dialog.ts b/polygerrit-ui/app/elements/admin/gr-create-pointer-dialog/gr-create-pointer-dialog.ts
index 889a859..558d571 100644
--- a/polygerrit-ui/app/elements/admin/gr-create-pointer-dialog/gr-create-pointer-dialog.ts
+++ b/polygerrit-ui/app/elements/admin/gr-create-pointer-dialog/gr-create-pointer-dialog.ts
@@ -6,8 +6,6 @@
 import '@polymer/iron-input/iron-input';
 import '../../shared/gr-button/gr-button';
 import '../../shared/gr-select/gr-select';
-import {encodeURL, getBaseUrl} from '../../../utils/url-util';
-import {page} from '../../../utils/page-wrapper-utils';
 import {BranchName, RepoName} from '../../../types/common';
 import {getAppContext} from '../../../services/app-context';
 import {formStyles} from '../../../styles/gr-form-styles';
@@ -15,7 +13,7 @@
 import {LitElement, PropertyValues, css, html} from 'lit';
 import {customElement, property, state} from 'lit/decorators.js';
 import {BindValueChangeEvent} from '../../../types/events';
-import {fireEvent} from '../../../utils/event-util';
+import {fireAlert, fireEvent, fireReload} from '../../../utils/event-util';
 import {RepoDetailView} from '../../../models/views/repo';
 
 declare global {
@@ -126,13 +124,13 @@
       throw new Error('itemName name is not set');
     }
     const USE_HEAD = this.itemRevision ? this.itemRevision : 'HEAD';
-    const url = `${getBaseUrl()}/admin/repos/${encodeURL(this.repoName, true)}`;
     if (this.itemDetail === RepoDetailView.BRANCHES) {
       return this.restApiService
         .createRepoBranch(this.repoName, this.itemName, {revision: USE_HEAD})
         .then(itemRegistered => {
           if (itemRegistered.status === 201) {
-            page.show(`${url},branches`);
+            fireAlert(this, 'Branch created successfully. Reloading...');
+            fireReload(this);
           }
         });
     } else if (this.itemDetail === RepoDetailView.TAGS) {
@@ -143,7 +141,8 @@
         })
         .then(itemRegistered => {
           if (itemRegistered.status === 201) {
-            page.show(`${url},tags`);
+            fireAlert(this, 'Tag created successfully. Reloading...');
+            fireReload(this);
           }
         });
     }
diff --git a/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts b/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts
index 64bfe91..2b7d1ff 100644
--- a/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts
+++ b/polygerrit-ui/app/elements/core/gr-error-manager/gr-error-manager.ts
@@ -528,6 +528,9 @@
     this.reporting.reportErrorDialog(message);
     this.errorDialog.text = message;
     this.errorDialog.showSignInButton = !!options && !!options.showSignInButton;
+    if (this.errorModal.hasAttribute('open')) {
+      this.errorModal.close();
+    }
     this.errorModal.showModal();
   }
 }
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-legacy.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-legacy.ts
index 090d125..5270603 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-legacy.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-legacy.ts
@@ -347,7 +347,8 @@
   createTextEl(
     lineNumberEl: HTMLElement | null,
     line: GrDiffLine,
-    side?: Side
+    side?: Side,
+    twoSlots?: boolean
   ) {
     const td = createElementDiff('td');
     if (line.type !== GrDiffLineType.BLANK) {
@@ -403,9 +404,19 @@
       const threadGroupEl = document.createElement('div');
       threadGroupEl.className = 'thread-group';
       threadGroupEl.setAttribute('data-side', side);
+
       const slot = document.createElement('slot');
       slot.name = `${side}-${lineNumber}`;
       threadGroupEl.appendChild(slot);
+
+      // For line.type === BOTH in unified diff we want two slots.
+      if (twoSlots) {
+        const slot = document.createElement('slot');
+        const otherSide = side === Side.LEFT ? Side.RIGHT : Side.LEFT;
+        slot.name = `${otherSide}-${line.lineNumber(otherSide)}`;
+        threadGroupEl.appendChild(slot);
+      }
+
       td.appendChild(threadGroupEl);
     }
 
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-unified.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-unified.ts
index f760232..ffc2dcd 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-unified.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-builder-unified.ts
@@ -142,7 +142,8 @@
         .join(' ')
         .trim()
     );
-    row.appendChild(this.createTextEl(lineNumberEl, line, side));
+    const twoSlots = line.type === GrDiffLineType.BOTH;
+    row.appendChild(this.createTextEl(lineNumberEl, line, side, twoSlots));
     return row;
   }
 
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
index e496cca..14b8280 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row.ts
@@ -348,7 +348,7 @@
           if (lineNumber)
             fire(this, 'line-mouse-leave', {lineNum: lineNumber, side});
         }}
-      >${this.renderText(side)}${this.renderThreadGroup(side, lineNumber)}</td>
+      >${this.renderText(side)}${this.renderThreadGroup(side)}</td>
     `;
   }
 
@@ -369,11 +369,21 @@
     return html`<td class=${diffClasses(...extras)}>${sign}</td>`;
   }
 
-  private renderThreadGroup(side: Side, lineNumber?: LineNumber) {
-    if (!lineNumber) return;
-    // .content has `white-space: pre`, so prettier must not add spaces.
-    // prettier-ignore
-    return html`<div class="thread-group" data-side=${side}><slot name="${side}-${lineNumber}"></slot></div>`;
+  private renderThreadGroup(side: Side) {
+    const lineNumber = this.lineNumber(side);
+    if (!lineNumber) return nothing;
+    return html`<div class="thread-group" data-side=${side}>
+      <slot name="${side}-${lineNumber}"></slot>
+      ${this.renderSecondSlot()}
+    </div>`;
+  }
+
+  private renderSecondSlot() {
+    if (!this.unifiedDiff) return nothing;
+    if (this.line(Side.LEFT)?.type !== GrDiffLineType.BOTH) return nothing;
+    return html`<slot
+      name="${Side.LEFT}-${this.lineNumber(Side.LEFT)}"
+    ></slot>`;
   }
 
   private contentRef(side: Side) {
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts
index 27fc920..1c7b311 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-builder/gr-diff-row_test.ts
@@ -93,6 +93,66 @@
     );
   });
 
+  test('both unified', async () => {
+    const line = new GrDiffLine(GrDiffLineType.BOTH, 1, 1);
+    line.text = 'lorem ipsum';
+    element.left = line;
+    element.right = line;
+    element.unifiedDiff = true;
+    await element.updateComplete;
+    assert.lightDom.equal(
+      element,
+      /* HTML */ `
+        <table>
+          <tbody>
+            <tr
+              aria-labelledby="left-button-1 right-button-1 right-content-1"
+              class="both diff-row gr-diff unified"
+              tabindex="-1"
+            >
+              <td class="blame gr-diff" data-line-number="1"></td>
+              <td class="gr-diff left lineNum" data-value="1">
+                <button
+                  aria-label="1 unmodified"
+                  class="gr-diff left lineNumButton"
+                  data-value="1"
+                  id="left-button-1"
+                  tabindex="-1"
+                >
+                  1
+                </button>
+              </td>
+              <td class="gr-diff lineNum right" data-value="1">
+                <button
+                  aria-label="1 unmodified"
+                  class="gr-diff lineNumButton right"
+                  data-value="1"
+                  id="right-button-1"
+                  tabindex="-1"
+                >
+                  1
+                </button>
+              </td>
+              <td class="both content gr-diff no-intraline-info right">
+                <div
+                  class="contentText gr-diff"
+                  data-side="right"
+                  id="right-content-1"
+                >
+                  <gr-diff-text> lorem ipsum </gr-diff-text>
+                </div>
+                <div class="thread-group" data-side="right">
+                  <slot name="right-1"> </slot>
+                  <slot name="left-1"> </slot>
+                </div>
+              </td>
+            </tr>
+          </tbody>
+        </table>
+      `
+    );
+  });
+
   test('add', async () => {
     const line = new GrDiffLine(GrDiffLineType.ADD, 0, 1);
     line.text = 'lorem ipsum';
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation.ts b/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation.ts
index 92175eb..38bd707 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation.ts
@@ -171,18 +171,20 @@
     cssClass: string,
     firstPart?: boolean
   ) {
-    if (this.getLength(node) === offset || offset === 0) {
-      return this.wrapInHighlight(node, cssClass);
-    } else {
-      if (firstPart) {
-        this.splitNode(node, offset);
-        // Node points to first part of the Text, second one is sibling.
-      } else {
-        // if node is Text then splitNode will return a Text
-        node = this.splitNode(node, offset) as Text;
-      }
+    if (
+      (this.getLength(node) === offset && firstPart) ||
+      (offset === 0 && !firstPart)
+    ) {
       return this.wrapInHighlight(node, cssClass);
     }
+    if (firstPart) {
+      this.splitNode(node, offset);
+      // Node points to first part of the Text, second one is sibling.
+    } else {
+      // if node is Text then splitNode will return a Text
+      node = this.splitNode(node, offset) as Text;
+    }
+    return this.wrapInHighlight(node, cssClass);
   },
 
   /**
@@ -225,7 +227,6 @@
    */
   splitTextNode(node: Text, offset: number) {
     if (node.textContent?.match(REGEX_ASTRAL_SYMBOL)) {
-      // TODO (viktard): Polyfill Array.from for IE10.
       const head = Array.from(node.textContent);
       const tail = head.splice(offset);
       const parent = node.parentNode;
diff --git a/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation_test.ts b/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation_test.ts
index fdf1785..f319a3c 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff-highlight/gr-annotation_test.ts
@@ -27,79 +27,77 @@
     str = textNode.textContent!;
   });
 
+  test('_annotateText length:0 offset:0', () => {
+    GrAnnotation._annotateText(textNode, 0, 0, 'foobar');
+
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      '<hl class="foobar"></hl>Lorem ipsum dolor sit amet, suspendisse inceptos vehicula'
+    );
+  });
+
+  test('_annotateText length:0 offset:1', () => {
+    GrAnnotation._annotateText(textNode, 1, 0, 'foobar');
+
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      'L<hl class="foobar"></hl>orem ipsum dolor sit amet, suspendisse inceptos vehicula'
+    );
+  });
+
+  test('_annotateText length:0 offset:str.length', () => {
+    GrAnnotation._annotateText(textNode, str.length, 0, 'foobar');
+
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      'Lorem ipsum dolor sit amet, suspendisse inceptos vehicula<hl class="foobar"></hl>'
+    );
+  });
+
   test('_annotateText Case 1', () => {
     GrAnnotation._annotateText(textNode, 0, str.length, 'foobar');
 
-    assert.equal(parent.childNodes.length, 1);
-    assert.instanceOf(parent.childNodes[0], HTMLElement);
-    const firstChild = parent.childNodes[0] as HTMLElement;
-    assert.equal(firstChild.className, 'foobar');
-    assert.instanceOf(firstChild.childNodes[0], Text);
-    assert.equal(firstChild.childNodes[0].textContent, str);
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      '<hl class="foobar">Lorem ipsum dolor sit amet, suspendisse inceptos vehicula</hl>'
+    );
   });
 
   test('_annotateText Case 2', () => {
-    const length = 12;
-    const substr = str.substr(0, length);
-    const remainder = str.substr(length);
+    GrAnnotation._annotateText(textNode, 0, 12, 'foobar');
 
-    GrAnnotation._annotateText(textNode, 0, length, 'foobar');
-
-    assert.equal(parent.childNodes.length, 2);
-
-    assert.instanceOf(parent.childNodes[0], HTMLElement);
-    const firstChild = parent.childNodes[0] as HTMLElement;
-    assert.equal(firstChild.className, 'foobar');
-    assert.instanceOf(firstChild.childNodes[0], Text);
-    assert.equal(firstChild.childNodes[0].textContent, substr);
-
-    assert.instanceOf(parent.childNodes[1], Text);
-    assert.equal(parent.childNodes[1].textContent, remainder);
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      '<hl class="foobar">Lorem ipsum </hl>dolor sit amet, suspendisse inceptos vehicula'
+    );
   });
 
   test('_annotateText Case 3', () => {
-    const index = 12;
-    const length = str.length - index;
-    const remainder = str.substr(0, index);
-    const substr = str.substr(index);
+    GrAnnotation._annotateText(textNode, 12, str.length - 12, 'foobar');
 
-    GrAnnotation._annotateText(textNode, index, length, 'foobar');
-
-    assert.equal(parent.childNodes.length, 2);
-
-    assert.instanceOf(parent.childNodes[0], Text);
-    assert.equal(parent.childNodes[0].textContent, remainder);
-
-    const secondChild = parent.childNodes[1] as HTMLElement;
-    assert.instanceOf(secondChild, HTMLElement);
-    assert.equal(secondChild.className, 'foobar');
-    assert.instanceOf(secondChild.childNodes[0], Text);
-    assert.equal(secondChild.childNodes[0].textContent, substr);
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      'Lorem ipsum <hl class="foobar">dolor sit amet, suspendisse inceptos vehicula</hl>'
+    );
   });
 
   test('_annotateText Case 4', () => {
     const index = str.indexOf('dolor');
     const length = 'dolor '.length;
 
-    const remainderPre = str.substr(0, index);
-    const substr = str.substr(index, length);
-    const remainderPost = str.substr(index + length);
-
     GrAnnotation._annotateText(textNode, index, length, 'foobar');
 
-    assert.equal(parent.childNodes.length, 3);
-
-    assert.instanceOf(parent.childNodes[0], Text);
-    assert.equal(parent.childNodes[0].textContent, remainderPre);
-
-    const secondChild = parent.childNodes[1] as HTMLElement;
-    assert.instanceOf(secondChild, HTMLElement);
-    assert.equal(secondChild.className, 'foobar');
-    assert.instanceOf(secondChild.childNodes[0], Text);
-    assert.equal(secondChild.childNodes[0].textContent, substr);
-
-    assert.instanceOf(parent.childNodes[2], Text);
-    assert.equal(parent.childNodes[2].textContent, remainderPost);
+    assert.equal(parent.textContent, str);
+    assert.equal(
+      parent.innerHTML,
+      'Lorem ipsum <hl class="foobar">dolor </hl>sit amet, suspendisse inceptos vehicula'
+    );
   });
 
   test('_annotateElement design doc example', () => {
@@ -116,45 +114,9 @@
     });
 
     assert.equal(parent.textContent, str);
-
-    // Layer 1:
-    const layer1 = parent.querySelectorAll<HTMLElement>('.layer-1');
-    assert.equal(layer1.length, 1);
-    assert.equal(layer1[0].textContent, layers[0]);
-    assert.equal(layer1[0].parentElement, parent);
-
-    // Layer 2:
-    const layer2 = parent.querySelectorAll<HTMLElement>('.layer-2');
-    assert.equal(layer2.length, 1);
-    assert.equal(layer2[0].textContent, layers[1]);
-    assert.equal(layer2[0].parentElement, parent);
-
-    // Layer 3:
-    const layer3 = parent.querySelectorAll<HTMLElement>('.layer-3');
-    assert.equal(layer3.length, 1);
-    assert.equal(layer3[0].textContent, layers[2]);
-    assert.equal(layer3[0].parentElement, layer1[0]);
-
-    // Layer 4:
-    const layer4 = parent.querySelectorAll<HTMLElement>('.layer-4');
-    assert.equal(layer4.length, 3);
-
-    assert.equal(layer4[0].textContent, 'et, ');
-    assert.equal(layer4[0].parentElement, layer3[0]);
-
-    assert.equal(layer4[1].textContent, 'suspendisse ');
-    assert.equal(layer4[1].parentElement, parent);
-
-    assert.equal(layer4[2].textContent, 'ince');
-    assert.equal(layer4[2].parentElement, layer2[0]);
-
     assert.equal(
-      [
-        layer4[0].textContent,
-        layer4[1].textContent,
-        layer4[2].textContent,
-      ].join(''),
-      layers[3]
+      parent.innerHTML,
+      'Lorem ipsum dolor sit <hl class="layer-1"><hl class="layer-3">am<hl class="layer-4">et, </hl></hl></hl><hl class="layer-4">suspendisse </hl><hl class="layer-2"><hl class="layer-4">ince</hl>ptos </hl>vehicula'
     );
   });
 
diff --git a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts
index bbe091f..ce1393d 100644
--- a/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-diff/gr-diff_test.ts
@@ -3218,6 +3218,7 @@
                       </div>
                       <div class="thread-group" data-side="right">
                         <slot name="right-FILE"> </slot>
+                        <slot name="left-FILE"> </slot>
                       </div>
                     </td>
                   </tr>
diff --git a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts
index 58f3f75..38eecfa 100644
--- a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts
+++ b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer.ts
@@ -144,12 +144,13 @@
       side,
       range,
       operation: (forLine, startChar, endChar) => {
-        forLine.push({
-          start: startChar,
-          end: endChar,
-          id: id(commentRange),
-          longRange,
-        });
+        if (startChar !== endChar)
+          forLine.push({
+            start: startChar,
+            end: endChar,
+            id: id(commentRange),
+            longRange,
+          });
       },
     });
   }
@@ -202,7 +203,7 @@
       // Normalize invalid ranges where the start is after the end but the
       // start still makes sense. Set the end to the end of the line.
       // @see Issue 5744
-      if (range.start >= range.end && range.start < line.text.length) {
+      if (range.start > range.end && range.start < line.text.length) {
         range.end = line.text.length;
       }
 
diff --git a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts
index 33515b25..7feda47 100644
--- a/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts
+++ b/polygerrit-ui/app/embed/diff/gr-ranged-comment-layer/gr-ranged-comment-layer_test.ts
@@ -69,6 +69,16 @@
   },
 };
 
+const rangeF: CommentRangeLayer = {
+  side: Side.RIGHT,
+  range: {
+    end_character: 0,
+    end_line: 24,
+    start_character: 0,
+    start_line: 23,
+  },
+};
+
 suite('gr-ranged-comment-layer', () => {
   let element: GrRangedCommentLayer;
 
@@ -79,6 +89,7 @@
       rangeC,
       rangeD,
       rangeE,
+      rangeF,
     ];
 
     element = new GrRangedCommentLayer();
@@ -219,6 +230,16 @@
       );
     });
 
+    test('do not annotate lines with end_character 0', () => {
+      line = new GrDiffLine(GrDiffLineType.BOTH);
+      line.afterNumber = 24;
+      el.setAttribute('data-side', Side.RIGHT);
+
+      element.annotate(el, lineNumberEl, line);
+
+      assert.isFalse(annotateElementStub.called);
+    });
+
     test('updateRanges remove all', () => {
       assertHasRange(rangeA, true);
       assertHasRange(rangeB, true);