diff --git a/.gitignore b/.gitignore
index fdefc8c..b657905 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,6 +1,7 @@
 .DS_Store
 *.log
-.nyc_output/
 coverage/
 node_modules/
+/lib/
+/index.js
 yarn.lock
diff --git a/.prettierignore b/.prettierignore
index 2ac20d2..619aa6b 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1,4 +1,3 @@
 coverage/
 *.html
-*.json
 *.md
diff --git a/index.js b/dev/index.js
similarity index 100%
rename from index.js
rename to dev/index.js
diff --git a/lib/html.js b/dev/lib/html.js
similarity index 100%
rename from lib/html.js
rename to dev/lib/html.js
diff --git a/lib/math-flow.js b/dev/lib/math-flow.js
similarity index 63%
rename from lib/math-flow.js
rename to dev/lib/math-flow.js
index 6a3b640..ca6c1a1 100644
--- a/lib/math-flow.js
+++ b/dev/lib/math-flow.js
@@ -1,4 +1,9 @@
+import assert from 'assert'
 import {factorySpace} from 'micromark-factory-space'
+import {markdownLineEnding} from 'micromark-util-character'
+import {codes} from 'micromark-util-symbol/codes.js'
+import {constants} from 'micromark-util-symbol/constants.js'
+import {types} from 'micromark-util-symbol/types.js'
 
 export const mathFlow = {
   tokenize: tokenizeMathFenced,
@@ -9,7 +14,7 @@ function tokenizeMathFenced(effects, ok, nok) {
   const self = this
   const tail = self.events[self.events.length - 1]
   const initialSize =
-    tail && tail[1].type === 'linePrefix'
+    tail && tail[1].type === types.linePrefix
       ? tail[2].sliceSerialize(tail[1], true).length
       : 0
   let sizeOpen = 0
@@ -17,9 +22,7 @@ function tokenizeMathFenced(effects, ok, nok) {
   return start
 
   function start(code) {
-    /* istanbul ignore if - handled by mm */
-    if (code !== 36) throw new Error('expected `$`')
-
+    assert(code === codes.dollarSign, 'expected `$`')
     effects.enter('mathFlow')
     effects.enter('mathFlowFence')
     effects.enter('mathFlowFenceSequence')
@@ -27,7 +30,7 @@ function tokenizeMathFenced(effects, ok, nok) {
   }
 
   function sequenceOpen(code) {
-    if (code === 36) {
+    if (code === codes.dollarSign) {
       effects.consume(code)
       sizeOpen++
       return sequenceOpen
@@ -36,27 +39,27 @@ function tokenizeMathFenced(effects, ok, nok) {
     effects.exit('mathFlowFenceSequence')
     return sizeOpen < 2
       ? nok(code)
-      : factorySpace(effects, metaOpen, 'whitespace')(code)
+      : factorySpace(effects, metaOpen, types.whitespace)(code)
   }
 
   function metaOpen(code) {
-    if (code === null || code === -5 || code === -4 || code === -3) {
+    if (code === codes.eof || markdownLineEnding(code)) {
       return openAfter(code)
     }
 
     effects.enter('mathFlowFenceMeta')
-    effects.enter('chunkString', {contentType: 'string'})
+    effects.enter(types.chunkString, {contentType: constants.contentTypeString})
     return meta(code)
   }
 
   function meta(code) {
-    if (code === null || code === -5 || code === -4 || code === -3) {
-      effects.exit('chunkString')
+    if (code === codes.eof || markdownLineEnding(code)) {
+      effects.exit(types.chunkString)
       effects.exit('mathFlowFenceMeta')
       return openAfter(code)
     }
 
-    if (code === 36) return nok(code)
+    if (code === codes.dollarSign) return nok(code)
     effects.consume(code)
     return meta
   }
@@ -67,19 +70,19 @@ function tokenizeMathFenced(effects, ok, nok) {
   }
 
   function content(code) {
-    if (code === null) {
+    if (code === codes.eof) {
       return after(code)
     }
 
-    if (code === -5 || code === -4 || code === -3) {
-      effects.enter('lineEnding')
+    if (markdownLineEnding(code)) {
+      effects.enter(types.lineEnding)
       effects.consume(code)
-      effects.exit('lineEnding')
+      effects.exit(types.lineEnding)
       return effects.attempt(
         {tokenize: tokenizeClosingFence, partial: true},
         after,
         initialSize
-          ? factorySpace(effects, content, 'linePrefix', initialSize + 1)
+          ? factorySpace(effects, content, types.linePrefix, initialSize + 1)
           : content
       )
     }
@@ -89,7 +92,7 @@ function tokenizeMathFenced(effects, ok, nok) {
   }
 
   function contentContinue(code) {
-    if (code === null || code === -5 || code === -4 || code === -3) {
+    if (code === codes.eof || markdownLineEnding(code)) {
       effects.exit('mathFlowValue')
       return content(code)
     }
@@ -106,7 +109,12 @@ function tokenizeMathFenced(effects, ok, nok) {
   function tokenizeClosingFence(effects, ok, nok) {
     let size = 0
 
-    return factorySpace(effects, closingPrefixAfter, 'linePrefix', 4)
+    return factorySpace(
+      effects,
+      closingPrefixAfter,
+      types.linePrefix,
+      constants.tabSize
+    )
 
     function closingPrefixAfter(code) {
       effects.enter('mathFlowFence')
@@ -115,7 +123,7 @@ function tokenizeMathFenced(effects, ok, nok) {
     }
 
     function closingSequence(code) {
-      if (code === 36) {
+      if (code === codes.dollarSign) {
         effects.consume(code)
         size++
         return closingSequence
@@ -123,11 +131,11 @@ function tokenizeMathFenced(effects, ok, nok) {
 
       if (size < sizeOpen) return nok(code)
       effects.exit('mathFlowFenceSequence')
-      return factorySpace(effects, closingSequenceEnd, 'whitespace')(code)
+      return factorySpace(effects, closingSequenceEnd, types.whitespace)(code)
     }
 
     function closingSequenceEnd(code) {
-      if (code === null || code === -5 || code === -4 || code === -3) {
+      if (code === codes.eof || markdownLineEnding(code)) {
         effects.exit('mathFlowFence')
         return ok(code)
       }
diff --git a/lib/math-text.js b/dev/lib/math-text.js
similarity index 72%
rename from lib/math-text.js
rename to dev/lib/math-text.js
index 3e9215a..24e5d58 100644
--- a/lib/math-text.js
+++ b/dev/lib/math-text.js
@@ -1,3 +1,8 @@
+import assert from 'assert'
+import {markdownLineEnding} from 'micromark-util-character'
+import {codes} from 'micromark-util-symbol/codes.js'
+import {types} from 'micromark-util-symbol/types.js'
+
 export const mathText = {
   tokenize: tokenizeMathText,
   resolve: resolveMathText,
@@ -12,9 +17,9 @@ function resolveMathText(events) {
 
   // If we start and end with an EOL or a space.
   if (
-    (events[headEnterIndex][1].type === 'lineEnding' ||
+    (events[headEnterIndex][1].type === types.lineEnding ||
       events[headEnterIndex][1].type === 'space') &&
-    (events[tailExitIndex][1].type === 'lineEnding' ||
+    (events[tailExitIndex][1].type === types.lineEnding ||
       events[tailExitIndex][1].type === 'space')
   ) {
     index = headEnterIndex
@@ -38,12 +43,15 @@ function resolveMathText(events) {
 
   while (++index <= tailExitIndex) {
     if (enter === undefined) {
-      if (index !== tailExitIndex && events[index][1].type !== 'lineEnding') {
+      if (
+        index !== tailExitIndex &&
+        events[index][1].type !== types.lineEnding
+      ) {
         enter = index
       }
     } else if (
       index === tailExitIndex ||
-      events[index][1].type === 'lineEnding'
+      events[index][1].type === types.lineEnding
     ) {
       events[enter][1].type = 'mathTextData'
 
@@ -64,8 +72,8 @@ function resolveMathText(events) {
 function previous(code) {
   // If there is a previous code, there will always be a tail.
   return (
-    code !== 36 ||
-    this.events[this.events.length - 1][1].type === 'characterEscape'
+    code !== codes.dollarSign ||
+    this.events[this.events.length - 1][1].type === types.characterEscape
   )
 }
 
@@ -78,21 +86,15 @@ function tokenizeMathText(effects, ok, nok) {
   return start
 
   function start(code) {
-    /* istanbul ignore if - handled by mm */
-    if (code !== 36) throw new Error('expected `$`')
-
-    /* istanbul ignore if - handled by mm */
-    if (!previous.call(self, self.previous)) {
-      throw new Error('expected correct previous')
-    }
-
+    assert(code === codes.dollarSign, 'expected `$`')
+    assert(previous.call(self, self.previous), 'expected correct previous')
     effects.enter('mathText')
     effects.enter('mathTextSequence')
     return openingSequence(code)
   }
 
   function openingSequence(code) {
-    if (code === 36) {
+    if (code === codes.dollarSign) {
       effects.consume(code)
       sizeOpen++
       return openingSequence
@@ -103,31 +105,30 @@ function tokenizeMathText(effects, ok, nok) {
   }
 
   function gap(code) {
-    // EOF.
-    if (code === null) {
+    if (code === codes.eof) {
       return nok(code)
     }
 
     // Closing fence?
     // Could also be data.
-    if (code === 36) {
+    if (code === codes.dollarSign) {
       token = effects.enter('mathTextSequence')
       size = 0
       return closingSequence(code)
     }
 
     // Tabs don’t work, and virtual spaces don’t make sense.
-    if (code === 32) {
+    if (code === codes.space) {
       effects.enter('space')
       effects.consume(code)
       effects.exit('space')
       return gap
     }
 
-    if (code === -5 || code === -4 || code === -3) {
-      effects.enter('lineEnding')
+    if (markdownLineEnding(code)) {
+      effects.enter(types.lineEnding)
       effects.consume(code)
-      effects.exit('lineEnding')
+      effects.exit(types.lineEnding)
       return gap
     }
 
@@ -136,15 +137,13 @@ function tokenizeMathText(effects, ok, nok) {
     return data(code)
   }
 
-  // In code.
+  // In math.
   function data(code) {
     if (
-      code === null ||
-      code === 32 ||
-      code === 36 ||
-      code === -5 ||
-      code === -4 ||
-      code === -3
+      code === codes.eof ||
+      code === codes.space ||
+      code === codes.dollarSign ||
+      markdownLineEnding(code)
     ) {
       effects.exit('mathTextData')
       return gap(code)
@@ -157,7 +156,7 @@ function tokenizeMathText(effects, ok, nok) {
   // Closing fence.
   function closingSequence(code) {
     // More.
-    if (code === 36) {
+    if (code === codes.dollarSign) {
       effects.consume(code)
       size++
       return closingSequence
diff --git a/dev/lib/syntax.js b/dev/lib/syntax.js
new file mode 100644
index 0000000..1edfa2f
--- /dev/null
+++ b/dev/lib/syntax.js
@@ -0,0 +1,8 @@
+import {codes} from 'micromark-util-symbol/codes.js'
+import {mathFlow} from './math-flow.js'
+import {mathText} from './math-text.js'
+
+export const math = {
+  flow: {[codes.dollarSign]: mathFlow},
+  text: {[codes.dollarSign]: mathText}
+}
diff --git a/lib/syntax.js b/lib/syntax.js
deleted file mode 100644
index 98c4138..0000000
--- a/lib/syntax.js
+++ /dev/null
@@ -1,7 +0,0 @@
-import {mathFlow} from './math-flow.js'
-import {mathText} from './math-text.js'
-
-export const math = {
-  flow: {36: mathFlow},
-  text: {36: mathText}
-}
diff --git a/package.json b/package.json
index e519c0e..d60d7b2 100644
--- a/package.json
+++ b/package.json
@@ -27,16 +27,24 @@
   "type": "module",
   "main": "index.js",
   "files": [
+    "dev/",
     "lib/",
     "index.js"
   ],
+  "exports": {
+    "development": "./dev/index.js",
+    "default": "./index.js"
+  },
   "dependencies": {
     "katex": "^0.13.0",
-    "micromark": "^3.0.0-alpha.2",
-    "micromark-factory-space": "^1.0.0-alpha.2"
+    "micromark-factory-space": "^1.0.0-alpha.2",
+    "micromark-util-character": "^1.0.0-alpha.2",
+    "micromark-util-symbol": "^1.0.0-alpha.2"
   },
   "devDependencies": {
     "c8": "^7.0.0",
+    "micromark": "^3.0.0-alpha.2",
+    "micromark-build": "^1.0.0-alpha.2",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
@@ -44,16 +52,11 @@
     "xo": "^0.39.0"
   },
   "scripts": {
+    "build": "micromark-build",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
     "test-api": "node --conditions development test/index.js",
     "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node --conditions development test/index.js",
-    "test": "npm run format && npm run test-coverage"
-  },
-  "nyc": {
-    "check-coverage": true,
-    "lines": 100,
-    "functions": 100,
-    "branches": 100
+    "test": "npm run build && npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
diff --git a/test/index.js b/test/index.js
index 9852261..61e51ec 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,7 +1,7 @@
 import test from 'tape'
 import katex from 'katex'
 import {micromark} from 'micromark'
-import {math as syntax, mathHtml as html} from '../index.js'
+import {math as syntax, mathHtml as html} from '../dev/index.js'
 
 test('markdown -> html (micromark)', (t) => {
   t.equal(