[docs] Fix some broken links (#12107)

docs/src/pages/demos/dialogs/dialogs.md

@@ -7,7 +7,7 @@ components: Dialog, DialogTitle, DialogContent, DialogContentText, DialogActions
 
 <p class="description">Dialogs inform users about a task and can contain critical information, require decisions, or involve multiple tasks.</p>
 
-A [Dialog](https://material.io/design/components/dialogs.html) is a type of [modal](/utils/modals) window that appears in front of app content to provide critical information or ask for a decision. Dialogs disable all app functionality when they appear, and remain on screen until confirmed, dismissed, or a required action has been taken.
+A [Dialog](https://material.io/design/components/dialogs.html) is a type of [modal](/utils/modal) window that appears in front of app content to provide critical information or ask for a decision. Dialogs disable all app functionality when they appear, and remain on screen until confirmed, dismissed, or a required action has been taken.
 
 Dialogs are purposefully interruptive, so they should be used sparingly.
 

docs/src/pages/guides/api/api.md

@@ -101,7 +101,7 @@ however, the `open` / `onClose` / `onOpen` combination is used for display relat
 
 ### boolean vs enum
 
-There are a couple of way to the variants of a component: with a *boolean*; or with an *enum*.
+There are two options to design the API for the variations of a component: with a *boolean*; or with an *enum*.
 For example, let's take a button that has different types. Each option has its pros and cons:
 
 - Option 1 *boolean*:

docs/src/pages/utils/portal/portal.md

@@ -9,7 +9,7 @@ components: Portal
 
 The children of the portal component will be appended to the `container` specified.
 
-The component is used internally by the [`Modal`](/utils/modals) component.
+The component is used internally by the [`Modal`](/utils/modal) and [`Popper`](/utils/popper) components.
 On the server, the content won't be rendered.
 You have to wait for the client side reconciliation to see the children.
 

packages/material-ui/src/Fade/Fade.js

@@ -17,7 +17,7 @@ const styles = {
 };
 
 /**
- * The Fade transition is used by the [Modal](/utils/modals) component.
+ * The Fade transition is used by the [Modal](/utils/modal) component.
  * It uses [react-transition-group](https://github.com/reactjs/react-transition-group) internally.
  */
 class Fade extends React.Component {

packages/material-ui/src/Grow/Grow.js

@@ -22,7 +22,8 @@ const styles = {
 };
 
 /**
- * The Grow transition is used by the [Popover](/utils/popovers) component.
+ * The Grow transition is used by the [Tooltip](/demos/tooltips) and
+ * [Popover](/utils/popover) components.
  * It uses [react-transition-group](https://github.com/reactjs/react-transition-group) internally.
  */
 class Grow extends React.Component {

packages/material-ui/src/Modal/Modal.js

@@ -40,6 +40,9 @@ if (process.env.NODE_ENV !== 'production' && !React.createContext) {
   throw new Error('Material-UI: react@16.3.0 or greater is required.');
 }
 
+/**
+ * This component shares many concepts with [react-overlays](https://react-bootstrap.github.io/react-overlays/#modals).
+ */
 class Modal extends React.Component {
   mountNode = null;
 

packages/material-ui/src/Modal/ModalManager.js

@@ -64,7 +64,7 @@ function removeContainerStyle(data, container) {
  * @ignore - do not document.
  *
  * Proper state managment for containers and the modals in those containers.
- * Simplified, but inspired by react-overlay's ModalManager class
+ * Simplified, but inspired by react-overlay's ModalManager class.
  * Used by the Modal to ensure proper styling of containers.
  */
 class ModalManager {

packages/material-ui/src/Popper/Popper.js

@@ -28,6 +28,9 @@ function getAnchorEl(anchorEl) {
   return typeof anchorEl === 'function' ? anchorEl() : anchorEl;
 }
 
+/**
+ * Poppers rely on the 3rd party library [Popper.js](https://github.com/FezVrasta/popper.js) for positioning.
+ */
 class Popper extends React.Component {
   popper = null;
 

pages/api/fade.md

@@ -9,7 +9,7 @@ title: Fade API
 
 <p class="description">The API documentation of the Fade React component.</p>
 
-The Fade transition is used by the [Modal](/utils/modals) component.
+The Fade transition is used by the [Modal](/utils/modal) component.
 It uses [react-transition-group](https://github.com/reactjs/react-transition-group) internally.
 
 ## Props

pages/api/grow.md

@@ -9,7 +9,8 @@ title: Grow API
 
 <p class="description">The API documentation of the Grow React component.</p>
 
-The Grow transition is used by the [Popover](/utils/popovers) component.
+The Grow transition is used by the [Tooltip](/demos/tooltips) and
+[Popover](/utils/popover) components.
 It uses [react-transition-group](https://github.com/reactjs/react-transition-group) internally.
 
 ## Props

pages/api/modal.md

@@ -9,7 +9,7 @@ title: Modal API
 
 <p class="description">The API documentation of the Modal React component.</p>
 
-
+This component shares many concepts with [react-overlays](https://react-bootstrap.github.io/react-overlays/#modals).
 
 ## Props
 

pages/api/popper.md

@@ -9,7 +9,7 @@ title: Popper API
 
 <p class="description">The API documentation of the Popper React component.</p>
 
-
+Poppers rely on the 3rd party library [Popper.js](https://github.com/FezVrasta/popper.js) for positioning.
 
 ## Props