diff --git a/packages/react-dom/src/__tests__/ReactDOMComponent-test.js b/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
index 53ad186761b74..6541293f51333 100644
--- a/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMComponent-test.js
@@ -2188,8 +2188,9 @@ describe('ReactDOMComponent', () => {
           );
         });
       }).toErrorDev([
-        'Warning: <tr> cannot appear as a child of ' +
-          '<div>.' +
+        'Warning: In HTML, <tr> cannot be a child of ' +
+          '<div>.\n' +
+          'This will cause a hydration error.' +
           '\n    in tr (at **)' +
           '\n    in div (at **)',
       ]);
@@ -2208,8 +2209,9 @@ describe('ReactDOMComponent', () => {
           );
         });
       }).toErrorDev(
-        'Warning: <p> cannot appear as a descendant ' +
-          'of <p>.' +
+        'Warning: In HTML, <p> cannot be a descendant ' +
+          'of <p>.\n' +
+          'This will cause a hydration error.' +
           // There is no outer `p` here because root container is not part of the stack.
           '\n    in p (at **)' +
           '\n    in span (at **)',
@@ -2241,22 +2243,25 @@ describe('ReactDOMComponent', () => {
           root.render(<Foo />);
         });
       }).toErrorDev([
-        'Warning: <tr> cannot appear as a child of ' +
+        'Warning: In HTML, <tr> cannot be a child of ' +
           '<table>. Add a <tbody>, <thead> or <tfoot> to your code to match the DOM tree generated ' +
-          'by the browser.' +
+          'by the browser.\n' +
+          'This will cause a hydration error.' +
           '\n    in tr (at **)' +
           '\n    in Row (at **)' +
           '\n    in table (at **)' +
           '\n    in Foo (at **)',
-        'Warning: Text nodes cannot appear as a ' +
-          'child of <tr>.' +
+        'Warning: In HTML, text nodes cannot be a ' +
+          'child of <tr>.\n' +
+          'This will cause a hydration error.' +
           '\n    in tr (at **)' +
           '\n    in Row (at **)' +
           '\n    in table (at **)' +
           '\n    in Foo (at **)',
-        'Warning: Whitespace text nodes cannot ' +
-          "appear as a child of <table>. Make sure you don't have any extra " +
-          'whitespace between tags on each line of your source code.' +
+        'Warning: In HTML, whitespace text nodes cannot ' +
+          "be a child of <table>. Make sure you don't have any extra " +
+          'whitespace between tags on each line of your source code.\n' +
+          'This will cause a hydration error.' +
           '\n    in table (at **)' +
           '\n    in Foo (at **)',
       ]);
@@ -2283,9 +2288,10 @@ describe('ReactDOMComponent', () => {
           root.render(<Foo> </Foo>);
         });
       }).toErrorDev([
-        'Warning: Whitespace text nodes cannot ' +
-          "appear as a child of <table>. Make sure you don't have any extra " +
-          'whitespace between tags on each line of your source code.' +
+        'Warning: In HTML, whitespace text nodes cannot ' +
+          "be a child of <table>. Make sure you don't have any extra " +
+          'whitespace between tags on each line of your source code.\n' +
+          'This will cause a hydration error.' +
           '\n    in table (at **)' +
           '\n    in Foo (at **)',
       ]);
@@ -2311,8 +2317,9 @@ describe('ReactDOMComponent', () => {
           );
         });
       }).toErrorDev([
-        'Warning: Text nodes cannot appear as a ' +
-          'child of <tr>.' +
+        'Warning: In HTML, text nodes cannot be a ' +
+          'child of <tr>.\n' +
+          'This will cause a hydration error.' +
           '\n    in tr (at **)' +
           '\n    in Row (at **)' +
           '\n    in tbody (at **)' +
diff --git a/packages/react-dom/src/__tests__/ReactDOMFloat-test.js b/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
index 64f79140917c8..31c1607cc149c 100644
--- a/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMFloat-test.js
@@ -523,7 +523,7 @@ describe('ReactDOMFloat', () => {
     }).toErrorDev(
       [
         'Cannot render <noscript> outside the main document. Try moving it into the root <head> tag.',
-        'Warning: <noscript> cannot appear as a child of <#document>.',
+        'Warning: In HTML, <noscript> cannot be a child of <#document>.',
       ],
       {withoutStack: 1},
     );
@@ -538,7 +538,7 @@ describe('ReactDOMFloat', () => {
       await waitForAll([]);
     }).toErrorDev([
       'Cannot render <template> outside the main document. Try moving it into the root <head> tag.',
-      'Warning: <template> cannot appear as a child of <html>.',
+      'Warning: In HTML, <template> cannot be a child of <html>.',
     ]);
 
     await expect(async () => {
@@ -551,7 +551,7 @@ describe('ReactDOMFloat', () => {
       await waitForAll([]);
     }).toErrorDev([
       'Cannot render a <style> outside the main document without knowing its precedence and a unique href key. React can hoist and deduplicate <style> tags if you provide a `precedence` prop along with an `href` prop that does not conflic with the `href` values used in any other hoisted <style> or <link rel="stylesheet" ...> tags.  Note that hoisting <style> tags is considered an advanced feature that most will not use directly. Consider moving the <style> tag to the <head> or consider adding a `precedence="default"` and `href="some unique resource identifier"`, or move the <style> to the <style> tag.',
-      'Warning: <style> cannot appear as a child of <html>.',
+      'Warning: In HTML, <style> cannot be a child of <html>.',
     ]);
 
     await expect(async () => {
@@ -574,7 +574,7 @@ describe('ReactDOMFloat', () => {
     }).toErrorDev(
       [
         'Cannot render a <link rel="stylesheet" /> outside the main document without knowing its precedence. Consider adding precedence="default" or moving it into the root <head> tag.',
-        'Warning: <link> cannot appear as a child of <#document>.',
+        'Warning: In HTML, <link> cannot be a child of <#document>.',
       ],
       {withoutStack: 1},
     );
@@ -591,7 +591,7 @@ describe('ReactDOMFloat', () => {
       await waitForAll([]);
     }).toErrorDev([
       'Cannot render a sync or defer <script> outside the main document without knowing its order. Try adding async="" or moving it into the root <head> tag.',
-      'Warning: <script> cannot appear as a child of <html>.',
+      'Warning: In HTML, <script> cannot be a child of <html>.',
     ]);
 
     await expect(async () => {
@@ -2552,11 +2552,11 @@ body {
       'Cannot render a <style> outside the main document if it has an `itemProp` prop. `itemProp` suggests the tag belongs to an `itemScope` which can appear anywhere in the DOM. If you were intending for React to hoist this <style> remove the `itemProp` prop. Otherwise, try moving this tag into the <head> or <body> of the Document.',
       'Cannot render a <link> outside the main document if it has an `itemProp` prop. `itemProp` suggests the tag belongs to an `itemScope` which can appear anywhere in the DOM. If you were intending for React to hoist this <link> remove the `itemProp` prop. Otherwise, try moving this tag into the <head> or <body> of the Document.',
       'Cannot render a <script> outside the main document if it has an `itemProp` prop. `itemProp` suggests the tag belongs to an `itemScope` which can appear anywhere in the DOM. If you were intending for React to hoist this <script> remove the `itemProp` prop. Otherwise, try moving this tag into the <head> or <body> of the Document.',
-      '<meta> cannot appear as a child of <html>',
-      '<title> cannot appear as a child of <html>',
-      '<style> cannot appear as a child of <html>',
-      '<link> cannot appear as a child of <html>',
-      '<script> cannot appear as a child of <html>',
+      'In HTML, <meta> cannot be a child of <html>',
+      'In HTML, <title> cannot be a child of <html>',
+      'In HTML, <style> cannot be a child of <html>',
+      'In HTML, <link> cannot be a child of <html>',
+      'In HTML, <script> cannot be a child of <html>',
     ]);
   });
 
diff --git a/packages/react-dom/src/__tests__/ReactDOMForm-test.js b/packages/react-dom/src/__tests__/ReactDOMForm-test.js
index 6cfd3201c1c24..000cfbf70c246 100644
--- a/packages/react-dom/src/__tests__/ReactDOMForm-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMForm-test.js
@@ -381,7 +381,8 @@ describe('ReactDOMForm', () => {
         );
       });
     }).toErrorDev([
-      'Warning: <form> cannot appear as a descendant of <form>.' +
+      'Warning: In HTML, <form> cannot be a descendant of <form>.\n' +
+        'This will cause a hydration error.' +
         '\n    in form (at **)' +
         '\n    in form (at **)',
     ]);
diff --git a/packages/react-dom/src/__tests__/ReactDOMOption-test.js b/packages/react-dom/src/__tests__/ReactDOMOption-test.js
index 66ab2b247eae4..abeae80125bdf 100644
--- a/packages/react-dom/src/__tests__/ReactDOMOption-test.js
+++ b/packages/react-dom/src/__tests__/ReactDOMOption-test.js
@@ -46,7 +46,8 @@ describe('ReactDOMOption', () => {
     expect(() => {
       node = ReactTestUtils.renderIntoDocument(el);
     }).toErrorDev(
-      '<div> cannot appear as a child of <option>.\n' +
+      'In HTML, <div> cannot be a child of <option>.\n' +
+        'This will cause a hydration error.\n' +
         '    in div (at **)\n' +
         '    in option (at **)',
     );
@@ -263,7 +264,7 @@ describe('ReactDOMOption', () => {
       [
         'Warning: Text content did not match. Server: "FooBaz" Client: "Foo"',
         'Warning: An error occurred during hydration. The server HTML was replaced with client content in <div>',
-        'Warning: <div> cannot appear as a child of <option>',
+        'Warning: In HTML, <div> cannot be a child of <option>',
       ],
       {withoutStack: 1},
     );
diff --git a/packages/react-dom/src/__tests__/validateDOMNesting-test.js b/packages/react-dom/src/__tests__/validateDOMNesting-test.js
index 971f186090b37..c79efe446a865 100644
--- a/packages/react-dom/src/__tests__/validateDOMNesting-test.js
+++ b/packages/react-dom/src/__tests__/validateDOMNesting-test.js
@@ -60,31 +60,42 @@ describe('validateDOMNesting', () => {
   it('prevents problematic nestings', () => {
     expectWarnings(
       ['a', 'a'],
-      ['<a> cannot appear as a descendant of <a>.\n' + '    in a (at **)'],
+      [
+        'In HTML, <a> cannot be a descendant of <a>.\n' +
+          'This will cause a hydration error.\n' +
+          '    in a (at **)',
+      ],
     );
     expectWarnings(
       ['form', 'form'],
       [
-        '<form> cannot appear as a descendant of <form>.\n' +
+        'In HTML, <form> cannot be a descendant of <form>.\n' +
+          'This will cause a hydration error.\n' +
           '    in form (at **)',
       ],
     );
     expectWarnings(
       ['p', 'p'],
-      ['<p> cannot appear as a descendant of <p>.\n' + '    in p (at **)'],
+      [
+        'In HTML, <p> cannot be a descendant of <p>.\n' +
+          'This will cause a hydration error.\n' +
+          '    in p (at **)',
+      ],
     );
     expectWarnings(
       ['table', 'tr'],
       [
-        '<tr> cannot appear as a child of <table>. ' +
+        'In HTML, <tr> cannot be a child of <table>. ' +
           'Add a <tbody>, <thead> or <tfoot> to your code to match the DOM tree generated by the browser.\n' +
+          'This will cause a hydration error.\n' +
           '    in tr (at **)',
       ],
     );
     expectWarnings(
       ['div', 'ul', 'li', 'div', 'li'],
       [
-        '<li> cannot appear as a descendant of <li>.\n' +
+        'In HTML, <li> cannot be a descendant of <li>.\n' +
+          'This will cause a hydration error.\n' +
           '    in li (at **)\n' +
           '    in div (at **)\n' +
           '    in li (at **)\n' +
@@ -93,16 +104,26 @@ describe('validateDOMNesting', () => {
     );
     expectWarnings(
       ['div', 'html'],
-      ['<html> cannot appear as a child of <div>.\n' + '    in html (at **)'],
+      [
+        'In HTML, <html> cannot be a child of <div>.\n' +
+          'This will cause a hydration error.\n' +
+          '    in html (at **)',
+      ],
     );
     expectWarnings(
       ['body', 'body'],
-      ['<body> cannot appear as a child of <body>.\n' + '    in body (at **)'],
+      [
+        'In HTML, <body> cannot be a child of <body>.\n' +
+          'This will cause a hydration error.\n' +
+          '    in body (at **)',
+      ],
     );
     expectWarnings(
       ['svg', 'foreignObject', 'body', 'p'],
       [
-        '<body> cannot appear as a child of <foreignObject>.\n' +
+        // TODO, this should say "In SVG",
+        'In HTML, <body> cannot be a child of <foreignObject>.\n' +
+          'This will cause a hydration error.' +
           '    in body (at **)\n' +
           '    in foreignObject (at **)',
         'Warning: You are mounting a new body component when a previous one has not first unmounted. It is an error to render more than one body component at a time and attributes and children of these components will likely fail in unpredictable ways. Please only render a single instance of <body> and if you need to mount a new one, ensure any previous ones have unmounted first.\n' +