diff --git a/contrib/render-a11y-string/render-a11y-string.js b/contrib/render-a11y-string/render-a11y-string.js
index 3cd7092e..fbc020ce 100644
--- a/contrib/render-a11y-string/render-a11y-string.js
+++ b/contrib/render-a11y-string/render-a11y-string.js
@@ -655,6 +655,11 @@ const handleObject = (
             break;
         }
 
+        case "html": {
+            buildA11yStrings(tree.body, a11yStrings, atomType);
+            break;
+        }
+
         default:
             (tree.type: empty);
             throw new Error("KaTeX a11y un-recognized type: " + tree.type);
diff --git a/docs/issues.md b/docs/issues.md
index 2bc23731..b3ca0ee0 100644
--- a/docs/issues.md
+++ b/docs/issues.md
@@ -22,6 +22,8 @@ title: Common Issues
 - MathJax defines `\color` to be like `\textcolor` by default; set KaTeX's
   `colorIsTextColor` option to `true` for this behavior.  KaTeX's default
   behavior matches MathJax with its `color.js` extension enabled.
+- Equivalents of MathJax `\class`, `\cssId`, and `\style` are `\htmlClass`,
+  `\htmlId`, and `\htmlStyle`, respectively, to avoid ambiguity.
 
 ## Troubleshooting
 
diff --git a/docs/options.md b/docs/options.md
index 4abe4b8d..3677e12a 100644
--- a/docs/options.md
+++ b/docs/options.md
@@ -28,6 +28,8 @@ You can provide an object of options as the last argument to [`katex.render` and
   - `"commentAtEnd"`: Use of `%` comment without a terminating newline.
     LaTeX would thereby comment out the end of math mode (e.g. `$`),
     causing an error.
+  - `"htmlExtension"`: Use of HTML extension (`\html`-prefixed) commands,
+    which are provieded for HTML manipulation.
 
   A second category of `errorCode`s never throw errors, but their strictness
   affects the behavior of KaTeX:
@@ -41,6 +43,10 @@ You can provide an object of options as the last argument to [`katex.render` and
   - `{command: "\\url", url, protocol}`
   - `{command: "\\href", url, protocol}`
   - `{command: "\\includegraphics", url, protocol}`
+  - `{command: "\\htmlClass", class}`
+  - `{command: "\\htmlId", id}`
+  - `{command: "\\htmlStyle", style}`
+  - `{command: "\\htmlData", attributes}`
 
   Here are some sample trust settings:
 
diff --git a/docs/support_table.md b/docs/support_table.md
index 8db08e45..fabe3835 100644
--- a/docs/support_table.md
+++ b/docs/support_table.md
@@ -458,6 +458,10 @@ use `\ce` instead|
 |\hskip|$w\hskip1em i\hskip2em d$|`w\hskip1em i\hskip2em d`|
 |\hslash|$\hslash$||
 |\hspace|$s\hspace7ex k$|`s\hspace7ex k`|
+|\htmlClass|$\htmlClass{foo}{x}$|`\htmlClass{foo}{x}` Must enable `trust` and disable `strict` [option](options.md)|
+|\htmlData|$\htmlData{foo=a, bar=b}{x}$|`\htmlData{foo=a, bar=b}{x}` Must enable `trust` and disable `strict` [option](options.md)|
+|\htmlId|$\htmlId{bar}{x}$|`\htmlId{bar}{x}` Must enable `trust` and disable `strict` [option](options.md)|
+|\htmlStyle|$\htmlStyle{color: red;}{x}$|`\htmlStyle{color: red;}{x}` Must enable `trust` and disable `strict` [option](options.md)|
 |\huge|$\huge huge$|`\huge huge`|
 |\Huge|$\Huge Huge$|`\Huge Huge`|
 
diff --git a/docs/supported.md b/docs/supported.md
index 10870350..b18686f7 100644
--- a/docs/supported.md
+++ b/docs/supported.md
@@ -113,9 +113,15 @@ or for just some URLs via the `trust` [option](options.md).
 | $\href{https://katex.org/}{\KaTeX}$ | `\href{https://katex.org/}{\KaTeX}` |
 | $\url{https://katex.org/}$ | `\url{https://katex.org/}` |
 | $\includegraphics[height=0.8em, totalheight=0.9em, width=0.9em, alt=KA logo]{https://katex.org/img/khan-academy.png}$ | `\includegraphics[height=0.8em, totalheight=0.9em, width=0.9em, alt=KA logo]{https://katex.org/img/khan-academy.png}` |
+| $\htmlId{bar}{x}$ | `\htmlId{bar}{x}` |
+| $\htmlClass{foo}{x}$ | `\htmlClass{foo}{x}` |
+| $\htmlStyle{color: red;}{x}$ | `\htmlStyle{color: red;}{x}` |
+| $\htmlData{foo=a, bar=b}{x}$ | `\htmlData{foo=a, bar=b}{x}` |
 
 `\includegraphics` supports `height`, `width`, `totalheight`, and `alt` in its first argument. `height` is required.
 
+HTML extension (`\html`-prefixed) commands are non-standard, so loosening `strict` option for `htmlExtension` is required.
+
 
 ## Letters and Unicode
 
diff --git a/src/Settings.js b/src/Settings.js
index e1707d71..4e0a2ec6 100644
--- a/src/Settings.js
+++ b/src/Settings.js
@@ -32,6 +32,22 @@ export type TrustContextTypes = {
         url: string,
         protocol?: string,
     |},
+    "\\htmlClass": {|
+        command: "\\htmlClass",
+        class: string,
+    |},
+    "\\htmlId": {|
+        command: "\\htmlId",
+        id: string,
+    |},
+    "\\htmlStyle": {|
+        command: "\\htmlStyle",
+        style: string,
+    |},
+    "\\htmlData": {|
+        command: "\\htmlData",
+        attributes: {[string]: string},
+    |},
 };
 export type AnyTrustContext = $Values<TrustContextTypes>;
 export type TrustFunction = (context: AnyTrustContext) => ?boolean;
diff --git a/src/buildHTML.js b/src/buildHTML.js
index 541b46f7..56186e19 100644
--- a/src/buildHTML.js
+++ b/src/buildHTML.js
@@ -9,7 +9,7 @@
 import ParseError from "./ParseError";
 import Style from "./Style";
 import buildCommon from "./buildCommon";
-import {Anchor} from "./domTree";
+import {Span, Anchor} from "./domTree";
 import utils from "./utils";
 import {spacings, tightSpacings} from "./spacingData";
 import {_htmlGroupBuilders as groupBuilders} from "./defineFunction";
@@ -185,8 +185,9 @@ const traverseNonSpaceNodes = function(
 // Check if given node is a partial group, i.e., does not affect spacing around.
 const checkPartialGroup = function(
     node: HtmlDomNode,
-): ?(DocumentFragment<HtmlDomNode> | Anchor) {
-    if (node instanceof DocumentFragment || node instanceof Anchor) {
+): ?(DocumentFragment<HtmlDomNode> | Anchor | DomSpan) {
+    if (node instanceof DocumentFragment || node instanceof Anchor
+        || (node instanceof Span && node.hasClass("enclosing"))) {
         return node;
     }
     return null;
diff --git a/src/functions.js b/src/functions.js
index 5bfae0eb..acb273e9 100644
--- a/src/functions.js
+++ b/src/functions.js
@@ -20,6 +20,7 @@ import "./functions/font";
 import "./functions/genfrac";
 import "./functions/horizBrace";
 import "./functions/href";
+import "./functions/html";
 import "./functions/htmlmathml";
 import "./functions/includegraphics";
 import "./functions/kern";
diff --git a/src/functions/html.js b/src/functions/html.js
new file mode 100644
index 00000000..c8d316aa
--- /dev/null
+++ b/src/functions/html.js
@@ -0,0 +1,102 @@
+// @flow
+import defineFunction, {ordargument} from "../defineFunction";
+import buildCommon from "../buildCommon";
+import {assertNodeType} from "../parseNode";
+import ParseError from "../ParseError";
+
+import * as html from "../buildHTML";
+import * as mml from "../buildMathML";
+
+defineFunction({
+    type: "html",
+    names: ["\\htmlClass", "\\htmlId", "\\htmlStyle", "\\htmlData"],
+    props: {
+        numArgs: 2,
+        argTypes: ["raw", "original"],
+        allowedInText: true,
+    },
+    handler: ({parser, funcName, token}, args) => {
+        const value = assertNodeType(args[0], "raw").string;
+        const body = args[1];
+
+        if (parser.settings.strict) {
+            parser.settings.reportNonstrict("htmlExtension",
+                "HTML extension is disabled on strict mode");
+        }
+
+        let trustContext;
+        const attributes = {};
+
+        switch (funcName) {
+            case "\\htmlClass":
+                attributes.class = value;
+                trustContext = {
+                    command: "\\htmlClass",
+                    class: value,
+                };
+                break;
+            case "\\htmlId":
+                attributes.id = value;
+                trustContext = {
+                    command: "\\htmlId",
+                    id: value,
+                };
+                break;
+            case "\\htmlStyle":
+                attributes.style = value;
+                trustContext = {
+                    command: "\\htmlStyle",
+                    style: value,
+                };
+                break;
+            case "\\htmlData": {
+                const data = value.split(",");
+                for (let i = 0; i < data.length; i++) {
+                    const keyVal = data[i].split("=");
+                    if (keyVal.length !== 2) {
+                        throw new ParseError(
+                            "Error parsing key-value for \\htmlData");
+                    }
+                    attributes["data-" + keyVal[0].trim()] = keyVal[1].trim();
+                }
+
+                trustContext = {
+                    command: "\\htmlData",
+                    attributes,
+                };
+                break;
+            }
+            default:
+                throw new Error("Unrecognized html command");
+        }
+
+        if (!parser.settings.isTrusted(trustContext)) {
+            return parser.formatUnsupportedCmd(funcName);
+        }
+        return {
+            type: "html",
+            mode: parser.mode,
+            attributes,
+            body: ordargument(body),
+        };
+    },
+    htmlBuilder: (group, options) => {
+        const elements = html.buildExpression(group.body, options, false);
+
+        const classes = ["enclosing"];
+        if (group.attributes.class) {
+            classes.push(...group.attributes.class.trim().split(/\s+/));
+        }
+
+        const span = buildCommon.makeSpan(classes, elements, options);
+        for (const attr in group.attributes) {
+            if (attr !== "class" && group.attributes.hasOwnProperty(attr)) {
+                span.setAttribute(attr, group.attributes[attr]);
+            }
+        }
+        return span;
+    },
+    mathmlBuilder: (group, options) => {
+        return mml.buildExpressionRow(group.body, options);
+    },
+});
diff --git a/src/parseNode.js b/src/parseNode.js
index b83d3dde..74852dd1 100644
--- a/src/parseNode.js
+++ b/src/parseNode.js
@@ -270,6 +270,13 @@ type ParseNodeTypes = {
         href: string,
         body: AnyParseNode[],
     |},
+    "html": {|
+        type: "html",
+        mode: Mode,
+        loc?: ?SourceLocation,
+        attributes: {[string]: string},
+        body: AnyParseNode[],
+    |},
     "htmlmathml": {|
         type: "htmlmathml",
         mode: Mode,
diff --git a/test/__snapshots__/katex-spec.js.snap b/test/__snapshots__/katex-spec.js.snap
index e3f30ccf..d8b2cd71 100755
--- a/test/__snapshots__/katex-spec.js.snap
+++ b/test/__snapshots__/katex-spec.js.snap
@@ -624,6 +624,226 @@ exports[`A parser that does not throw on unsupported commands should properly es
 
 `;
 
+exports[`An HTML extension builder should not affect spacing 1`] = `
+[
+  {
+    "attributes": {
+      "id": "a"
+    },
+    "children": [
+      {
+        "classes": [
+          "mord",
+          "mathdefault"
+        ],
+        "depth": 0,
+        "height": 0.43056,
+        "italic": 0,
+        "maxFontSize": 1,
+        "skew": 0.02778,
+        "style": {
+        },
+        "text": "x",
+        "width": 0.57153
+      },
+      {
+        "attributes": {
+        },
+        "children": [
+        ],
+        "classes": [
+          "mspace"
+        ],
+        "depth": 0,
+        "height": 0,
+        "maxFontSize": 0,
+        "style": {
+          "marginRight": "0.2222222222222222em"
+        }
+      },
+      {
+        "classes": [
+          "mbin"
+        ],
+        "depth": 0.08333,
+        "height": 0.58333,
+        "italic": 0,
+        "maxFontSize": 1,
+        "skew": 0,
+        "style": {
+        },
+        "text": "+",
+        "width": 0.77778
+      },
+      {
+        "attributes": {
+        },
+        "children": [
+        ],
+        "classes": [
+          "mspace"
+        ],
+        "depth": 0,
+        "height": 0,
+        "maxFontSize": 0,
+        "style": {
+          "marginRight": "0.2222222222222222em"
+        }
+      }
+    ],
+    "classes": [
+      "enclosing"
+    ],
+    "depth": 0.08333,
+    "height": 0.58333,
+    "maxFontSize": 1,
+    "style": {
+    }
+  },
+  {
+    "classes": [
+      "mord",
+      "mathdefault"
+    ],
+    "depth": 0.19444,
+    "height": 0.43056,
+    "italic": 0.03588,
+    "maxFontSize": 1,
+    "skew": 0.05556,
+    "style": {
+    },
+    "text": "y",
+    "width": 0.49028
+  }
+]
+`;
+
+exports[`An HTML extension builder should render with trust and strict setting 1`] = `
+[
+  {
+    "attributes": {
+      "id": "bar"
+    },
+    "children": [
+      {
+        "classes": [
+          "mord",
+          "mathdefault"
+        ],
+        "depth": 0,
+        "height": 0.43056,
+        "italic": 0,
+        "maxFontSize": 1,
+        "skew": 0.02778,
+        "style": {
+        },
+        "text": "x",
+        "width": 0.57153
+      }
+    ],
+    "classes": [
+      "enclosing"
+    ],
+    "depth": 0,
+    "height": 0.43056,
+    "maxFontSize": 1,
+    "style": {
+    }
+  },
+  {
+    "attributes": {
+    },
+    "children": [
+      {
+        "classes": [
+          "mord",
+          "mathdefault"
+        ],
+        "depth": 0,
+        "height": 0.43056,
+        "italic": 0,
+        "maxFontSize": 1,
+        "skew": 0.02778,
+        "style": {
+        },
+        "text": "x",
+        "width": 0.57153
+      }
+    ],
+    "classes": [
+      "enclosing",
+      "foo"
+    ],
+    "depth": 0,
+    "height": 0.43056,
+    "maxFontSize": 1,
+    "style": {
+    }
+  },
+  {
+    "attributes": {
+      "style": "color: red;"
+    },
+    "children": [
+      {
+        "classes": [
+          "mord",
+          "mathdefault"
+        ],
+        "depth": 0,
+        "height": 0.43056,
+        "italic": 0,
+        "maxFontSize": 1,
+        "skew": 0.02778,
+        "style": {
+        },
+        "text": "x",
+        "width": 0.57153
+      }
+    ],
+    "classes": [
+      "enclosing"
+    ],
+    "depth": 0,
+    "height": 0.43056,
+    "maxFontSize": 1,
+    "style": {
+    }
+  },
+  {
+    "attributes": {
+      "data-bar": "b",
+      "data-foo": "a"
+    },
+    "children": [
+      {
+        "classes": [
+          "mord",
+          "mathdefault"
+        ],
+        "depth": 0,
+        "height": 0.43056,
+        "italic": 0,
+        "maxFontSize": 1,
+        "skew": 0.02778,
+        "style": {
+        },
+        "text": "x",
+        "width": 0.57153
+      }
+    ],
+    "classes": [
+      "enclosing"
+    ],
+    "depth": 0,
+    "height": 0.43056,
+    "maxFontSize": 1,
+    "style": {
+    }
+  }
+]
+`;
+
 exports[`An implicit group parser within optional groups should work style commands \\sqrt[\\textstyle 3]{x} 1`] = `
 [
   {
diff --git a/test/katex-spec.js b/test/katex-spec.js
index 7f474eb4..da1b6430 100644
--- a/test/katex-spec.js
+++ b/test/katex-spec.js
@@ -2011,6 +2011,36 @@ describe("An includegraphics builder", function() {
     });
 });
 
+describe("An HTML extension builder", function() {
+    const html =
+        "\\htmlId{bar}{x}\\htmlClass{foo}{x}\\htmlStyle{color: red;}{x}\\htmlData{foo=a, bar=b}{x}";
+    const trustNonStrictSettings = new Settings({trust: true, strict: false});
+    it("should not fail", function() {
+        expect(html).toBuild(trustNonStrictSettings);
+    });
+
+    it("should set HTML attributes", function() {
+        const built = getBuilt(html, trustNonStrictSettings);
+        expect(built[0].attributes.id).toMatch("bar");
+        expect(built[1].classes).toContain("foo");
+        expect(built[2].attributes.style).toMatch("color: red");
+        expect(built[3].attributes).toEqual({
+            "data-bar": "b",
+            "data-foo": "a",
+        });
+    });
+
+    it("should not affect spacing", function() {
+        const built = getBuilt("\\htmlId{a}{x+}y", trustNonStrictSettings);
+        expect(built).toMatchSnapshot();
+    });
+
+    it("should render with trust and strict setting", function() {
+        const built = getBuilt(html, trustNonStrictSettings);
+        expect(built).toMatchSnapshot();
+    });
+});
+
 describe("A bin builder", function() {
     it("should create mbins normally", function() {
         const built = getBuilt`x + y`;
diff --git a/test/screenshotter/images/HTML-chrome.png b/test/screenshotter/images/HTML-chrome.png
new file mode 100644
index 00000000..52afcd6e
Binary files /dev/null and b/test/screenshotter/images/HTML-chrome.png differ
diff --git a/test/screenshotter/images/HTML-firefox.png b/test/screenshotter/images/HTML-firefox.png
new file mode 100644
index 00000000..e1646ea3
Binary files /dev/null and b/test/screenshotter/images/HTML-firefox.png differ
diff --git a/test/screenshotter/ss_data.yaml b/test/screenshotter/ss_data.yaml
index 8144c36d..e33c3bc7 100644
--- a/test/screenshotter/ss_data.yaml
+++ b/test/screenshotter/ss_data.yaml
@@ -149,6 +149,9 @@ GroupMacros:
         \endExp: \egroup
     tex: \startExp a+b\endExp
 HorizontalBraces: \overbrace{\displaystyle{\oint_S{\vec E\cdot\hat n\,\mathrm d a}}}^\text{emf} = \underbrace{\frac{q_{\text{enc}}}{\varepsilon_0}}_{\text{charge}}
+HTML:
+    tex: \htmlId{a}{a+}b\htmlStyle{color:red;}{+c}
+    nolatex: HTML extension not supported by LaTeX
 Includegraphics: |
     \def\logo{\includegraphics[height=0.8em, totalheight=0.9em, width=0.9em, alt=KA logo]{../../website/static/img/khan-academy.png}}
     \def\logoB{\includegraphics[height=0.4em, totalheight=0.9em, width=0.9em, alt=KA logo]{../../website/static/img/khan-academy.png}}
diff --git a/test/screenshotter/test.html b/test/screenshotter/test.html
index 6809558b..eb810b43 100644
--- a/test/screenshotter/test.html
+++ b/test/screenshotter/test.html
@@ -71,6 +71,7 @@
         var settings = {
             displayMode: !!query["display"],
             throwOnError: !query["noThrow"],
+            strict: false,
             trust: true  // trust test inputs
         };
         if (query["errorColor"]) {
diff --git a/website/lib/remarkable-katex.js b/website/lib/remarkable-katex.js
index afd50bd2..d6007354 100644
--- a/website/lib/remarkable-katex.js
+++ b/website/lib/remarkable-katex.js
@@ -30,7 +30,7 @@ module.exports = function(md, options) {
 
     function renderKatex(source, displayMode) {
         return katex.renderToString(source,
-            {displayMode, throwOnError: false, trust: true});
+            {displayMode, throwOnError: false, trust: true, strict: false});
     }
 
     /**