[MDX] Support YAML frontmatter (#3995)

* chore: remove old comment

* deps: add remark-frontmatter

* deps: add remark-mdx-frontmatter

* fix: handle null or undefined frontmatter key

* feat: configure frontmatter plugins with defaults

* test: frontmatter and custom frontmatter name

* docs: add frontmatterOptions config

* docs: add "variables" and "frontmatter" docs

* chore: excessible -> accessible

* chore: changeset

* chore: remove bad mdx comment

1 files changed, 156 insertions, 7 deletions

diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 82eb5671b..16775dabe 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -2074,13 +2074,17 @@ importers:
       es-module-lexer: ^0.10.5
       linkedom: ^0.14.12
       mocha: ^9.2.2
+      remark-frontmatter: ^4.0.1
       remark-gfm: ^3.0.1
+      remark-mdx-frontmatter: ^2.0.2
       remark-smartypants: ^2.0.0
       remark-toc: ^8.0.1
     dependencies:
       '@mdx-js/rollup': 2.1.2
       es-module-lexer: 0.10.5
+      remark-frontmatter: 4.0.1
       remark-gfm: 3.0.1
+      remark-mdx-frontmatter: 2.0.2
       remark-smartypants: 2.0.0
     devDependencies:
       '@types/chai': 4.3.1
@@ -4260,6 +4264,10 @@ packages:
       '@babel/helper-validator-identifier': 7.18.6
       to-fast-properties: 2.0.0
 
+  /@bcoe/v8-coverage/0.2.3:
+    resolution: {integrity: sha512-0hYQ8SB4Db5zvZB4axdMHGwEaQjkZzFjQiN9LVYvIFB2nSUHW9tYpxWriPrWDASIxiaXax83REcLxuSdnGPZtw==}
+    dev: false
+
   /@builder.io/partytown/0.4.5:
     resolution: {integrity: sha512-HcHlmMYSpOxfJ0lFVxgZrvgIjz1Q8knlGuWkBpvjIp68j+xVWg969+sn7BCfyKhcGaYlnVOY/CEBHapQBcl0jw==}
     hasBin: true
@@ -4759,6 +4767,11 @@ packages:
       '@babel/runtime': 7.18.6
     dev: false
 
+  /@istanbuljs/schema/0.1.3:
+    resolution: {integrity: sha512-ZXRY4jNvVgSVQ8DL3LTcakaAtXwTVUxE81hslsyD2AtoXW/wVob10HkOJ1X/pAlcI7D+2YoZKg5do8G/w6RYgA==}
+    engines: {node: '>=8'}
+    dev: false
+
   /@jridgewell/gen-mapping/0.1.1:
     resolution: {integrity: sha512-sQXCasFk+U8lWYEe66WxRDOE9PjVz4vSM51fTu3Hw+ClTpUSQb718772vH3pyS5pShp6lvQM7SxgIDXXXmOX7w==}
     engines: {node: '>=6.0.0'}
@@ -8108,6 +8121,10 @@ packages:
       ci-info: 3.3.2
     dev: true
 
+  /@types/istanbul-lib-coverage/2.0.4:
+    resolution: {integrity: sha512-z/QT1XN4K4KYuslS23k62yDIDLwLFkzxOuMplDtObz0+y7VqJCaO2o+SPwHCvLFZh7xazvvoor2tA/hPz9ee7g==}
+    dev: false
+
   /@types/json-schema/7.0.11:
     resolution: {integrity: sha512-wOuvG1SN4Us4rez+tylwwwCV1psiNVOkJeM3AUWUNWg/jDQY2+HE/444y5gc+jBmRqASOm2Oeh5c1axHobwRKQ==}
     dev: true
@@ -9174,6 +9191,25 @@ packages:
     engines: {node: '>= 0.8'}
     dev: true
 
+  /c8/7.12.0:
+    resolution: {integrity: sha512-CtgQrHOkyxr5koX1wEUmN/5cfDa2ckbHRA4Gy5LAL0zaCFtVWJS5++n+w4/sr2GWGerBxgTjpKeDclk/Qk6W/A==}
+    engines: {node: '>=10.12.0'}
+    hasBin: true
+    dependencies:
+      '@bcoe/v8-coverage': 0.2.3
+      '@istanbuljs/schema': 0.1.3
+      find-up: 5.0.0
+      foreground-child: 2.0.0
+      istanbul-lib-coverage: 3.2.0
+      istanbul-lib-report: 3.0.0
+      istanbul-reports: 3.1.5
+      rimraf: 3.0.2
+      test-exclude: 6.0.0
+      v8-to-istanbul: 9.0.1
+      yargs: 16.2.0
+      yargs-parser: 20.2.9
+    dev: false
+
   /cac/6.7.12:
     resolution: {integrity: sha512-rM7E2ygtMkJqD9c7WnFU6fruFcN3xe4FM5yUmgxhZzIKJk4uHl9U/fhwdajGFQbQuv43FAUo1Fe8gX/oIKDeSA==}
     engines: {node: '>=8'}
@@ -9374,7 +9410,6 @@ packages:
       string-width: 4.2.3
       strip-ansi: 6.0.1
       wrap-ansi: 7.0.0
-    dev: true
 
   /clone/1.0.4:
     resolution: {integrity: sha512-JQHZ2QMW6l3aH/j6xCqQThY/9OH4D/9ls34cgkUBiEeocRTU04tHfKPBsUK1PqZCUQM7GiA0IIXJSuXHI64Kbg==}
@@ -10390,6 +10425,13 @@ packages:
     resolution: {integrity: sha512-rxZj1GkQhY4x1j/CSnybK9cGuMFQYFPLq0iNyopqf14aOVLFtMv7Esika+ObJWPWiOHuMOAHz3YkWoLYYRnzWQ==}
     dev: false
 
+  /estree-util-value-to-estree/1.3.0:
+    resolution: {integrity: sha512-Y+ughcF9jSUJvncXwqRageavjrNPAI+1M/L3BI3PyLp1nmgYTGUXU6t5z1Y7OWuThoDdhPME07bQU+d5LxdJqw==}
+    engines: {node: '>=12.0.0'}
+    dependencies:
+      is-plain-obj: 3.0.0
+    dev: false
+
   /estree-util-visit/1.1.0:
     resolution: {integrity: sha512-3lXJ4Us9j8TUif9cWcQy81t9p5OLasnDuuhrFiqb+XstmKC1d1LmrQWYsY49/9URcfHE64mPypDBaNK9NwWDPQ==}
     dependencies:
@@ -10526,6 +10568,12 @@ packages:
     dependencies:
       reusify: 1.0.4
 
+  /fault/2.0.1:
+    resolution: {integrity: sha512-WtySTkS4OKev5JtpHXnib4Gxiurzh5NCGvWrFaZ34m6JehfTUhKZvn9njTfw48t6JumVQOmrKqpmGcdwxnhqBQ==}
+    dependencies:
+      format: 0.2.2
+    dev: false
+
   /fetch-blob/3.2.0:
     resolution: {integrity: sha512-7yAQpD2UMJzLi1Dqv7qFYnPbaPx7ZfFK6PiIxQ4PfkGPyNyl2Ugx+a/umUonmKqjhM4DnfbMvdX6otXq83soQQ==}
     engines: {node: ^12.20 || >= 14.13}
@@ -10624,6 +10672,19 @@ packages:
       is-callable: 1.2.4
     dev: false
 
+  /foreground-child/2.0.0:
+    resolution: {integrity: sha512-dCIq9FpEcyQyXKCkyzmlPTFNgrCzPudOe+mhvJU5zAtlBnGVy2yKxtfsxK2tQBThwq225jcvBjpw1Gr40uzZCA==}
+    engines: {node: '>=8.0.0'}
+    dependencies:
+      cross-spawn: 7.0.3
+      signal-exit: 3.0.7
+    dev: false
+
+  /format/0.2.2:
+    resolution: {integrity: sha512-wzsgA6WOq+09wrU1tsJ09udeR/YZRaeArL9e1wPbFg3GG2yDnC2ldKpxs4xunpFF9DgqCqOIra3bc1HWrJ37Ww==}
+    engines: {node: '>=0.4.x'}
+    dev: false
+
   /formdata-polyfill/4.0.10:
     resolution: {integrity: sha512-buewHzMvYL29jdeQTVILecSaZKnt/RJWjoZCF5OW60Z67/GmSLBkOFM7qh1PI3zFNtJbaZL5eQu1vLfazOwj4g==}
     engines: {node: '>=12.20.0'}
@@ -10749,7 +10810,6 @@ packages:
   /get-caller-file/2.0.5:
     resolution: {integrity: sha512-DyFP3BM/3YHTQOCUL/w0OZHR0lpKeGrxotcHWcqNEdnltqFwXVfhEBQ94eIo34AfQpo0rGki4cyIiftY06h2Fg==}
     engines: {node: 6.* || 8.* || >= 10.*}
-    dev: true
 
   /get-func-name/2.0.0:
     resolution: {integrity: sha512-Hm0ixYtaSZ/V7C8FJrtZIuBBI+iSgL+1Aq82zSu8VQNB4S3Gk8e7Qs3VwBDJAhmRZcFqkl3tQu36g/Foh5I5ig==}
@@ -11134,6 +11194,10 @@ packages:
     resolution: {integrity: sha512-DV5Ln36z34NNTDgnz0EWGBLZENelNAtkiFA4kyNOG2tDI6Mz1uSWiq1wAKdyjnJwyDiDO7Fa2SO1CTxPXL8VxA==}
     dev: false
 
+  /html-escaper/2.0.2:
+    resolution: {integrity: sha512-H2iMtd0I4Mt5eYiapRdIDjp+XzelXQ0tFE4JS7YFwFevXXMmOp9myNrUvCg0D6ws8iqkRPBfKHgbwig1SmlLfg==}
+    dev: false
+
   /html-escaper/3.0.3:
     resolution: {integrity: sha512-RuMffC89BOWQoY0WKGpIhn5gX3iI54O6nRA0yC124NYVtzjmFWBIiFd8M0x+ZdX0P9R4lADg1mgP8C7PxGOWuQ==}
 
@@ -11483,6 +11547,11 @@ packages:
     engines: {node: '>=8'}
     dev: true
 
+  /is-plain-obj/3.0.0:
+    resolution: {integrity: sha512-gwsOE28k+23GP1B6vFl1oVh/WOzmawBrKwo5Ev6wMKzPkaXaCDIQKzLnvsA42DRlbVTWorkgTKIviAKCWkfUwA==}
+    engines: {node: '>=10'}
+    dev: false
+
   /is-plain-obj/4.1.0:
     resolution: {integrity: sha512-+Pgi+vMuUNkJyExiMBt5IlFoMyKnr5zhJ4Uspz58WOhBF5QoIZkFyNHIbBAtHwzVAgk5RtndVNsDRN61/mmDqg==}
     engines: {node: '>=12'}
@@ -11596,6 +11665,28 @@ packages:
   /isexe/2.0.0:
     resolution: {integrity: sha512-RHxMLp9lnKHGHRng9QFhRCMbYAcVpn69smSGcq3f36xjgVVWThj4qqLbTLlq7Ssj8B+fIQ1EuCEGI2lKsyQeIw==}
 
+  /istanbul-lib-coverage/3.2.0:
+    resolution: {integrity: sha512-eOeJ5BHCmHYvQK7xt9GkdHuzuCGS1Y6g9Gvnx3Ym33fz/HpLRYxiS0wHNr+m/MBC8B647Xt608vCDEvhl9c6Mw==}
+    engines: {node: '>=8'}
+    dev: false
+
+  /istanbul-lib-report/3.0.0:
+    resolution: {integrity: sha512-wcdi+uAKzfiGT2abPpKZ0hSU1rGQjUQnLvtY5MpQ7QCTahD3VODhcu4wcfY1YtkGaDD5yuydOLINXsfbus9ROw==}
+    engines: {node: '>=8'}
+    dependencies:
+      istanbul-lib-coverage: 3.2.0
+      make-dir: 3.1.0
+      supports-color: 7.2.0
+    dev: false
+
+  /istanbul-reports/3.1.5:
+    resolution: {integrity: sha512-nUsEMa9pBt/NOHqbcbeJEgqIlY/K7rVWUX6Lql2orY5e9roQOthbR3vtY4zzf2orPELg80fnxxk9zUyPlgwD1w==}
+    engines: {node: '>=8'}
+    dependencies:
+      html-escaper: 2.0.2
+      istanbul-lib-report: 3.0.0
+    dev: false
+
   /jake/10.8.5:
     resolution: {integrity: sha512-sVpxYeuAhWt0OTWITwT98oyV0GsXyMlXCF+3L1SuafBVUIr/uILGRB+NqwkzhgXKvoJpDIpQvqkUALgdmQsQxw==}
     engines: {node: '>=10'}
@@ -11969,6 +12060,12 @@ packages:
       - supports-color
     dev: false
 
+  /mdast-util-frontmatter/1.0.0:
+    resolution: {integrity: sha512-7itKvp0arEVNpCktOET/eLFAYaZ+0cNjVtFtIPxgQ5tV+3i+D4SDDTjTzPWl44LT59PC+xdx+glNTawBdF98Mw==}
+    dependencies:
+      micromark-extension-frontmatter: 1.0.0
+    dev: false
+
   /mdast-util-gfm-autolink-literal/1.0.2:
     resolution: {integrity: sha512-FzopkOd4xTTBeGXhXSBU0OCDDh5lUj2rd+HQqG92Ld+jL4lpUfgX2AT2OHAVP9aEeDKp7G92fuooSZcYJA3cRg==}
     dependencies:
@@ -12179,6 +12276,14 @@ packages:
       uvu: 0.5.6
     dev: false
 
+  /micromark-extension-frontmatter/1.0.0:
+    resolution: {integrity: sha512-EXjmRnupoX6yYuUJSQhrQ9ggK0iQtQlpi6xeJzVD5xscyAI+giqco5fdymayZhJMbIFecjnE2yz85S9NzIgQpg==}
+    dependencies:
+      fault: 2.0.1
+      micromark-util-character: 1.1.0
+      micromark-util-symbol: 1.0.1
+    dev: false
+
   /micromark-extension-gfm-autolink-literal/1.0.3:
     resolution: {integrity: sha512-i3dmvU0htawfWED8aHMMAzAVp/F0Z+0bPh3YrbTPPL1v4YAlCZpy5rBO5p0LPYiZo0zFVkoYh7vDU7yQSiCMjg==}
     dependencies:
@@ -14080,6 +14185,15 @@ packages:
       unist-util-visit: 1.4.1
     dev: true
 
+  /remark-frontmatter/4.0.1:
+    resolution: {integrity: sha512-38fJrB0KnmD3E33a5jZC/5+gGAC2WKNiPw1/fdXJvijBlhA7RCsvJklrYJakS0HedninvaCYW8lQGf9C918GfA==}
+    dependencies:
+      '@types/mdast': 3.0.10
+      mdast-util-frontmatter: 1.0.0
+      micromark-extension-frontmatter: 1.0.0
+      unified: 10.1.2
+    dev: false
+
   /remark-gfm/3.0.1:
     resolution: {integrity: sha512-lEFDoi2PICJyNrACFOfDD3JlLkuSbOa5Wd8EPt06HUdptv8Gn0bxYTdbU/XXQ3swAPkEaGxxPN9cbnMHvVu1Ig==}
     dependencies:
@@ -14091,6 +14205,19 @@ packages:
       - supports-color
     dev: false
 
+  /remark-mdx-frontmatter/2.0.2:
+    resolution: {integrity: sha512-kxXltmWCo10x8JGtlaw16pJUF593R+b9UJILk/yp5mdU6PKfg9BLAZvoF5YVdP+sjzEDD0nGYVKcZDyJSbCHbw==}
+    engines: {node: '>=14.0.0'}
+    dependencies:
+      '@types/mdast': 3.0.10
+      c8: 7.12.0
+      estree-util-is-identifier-name: 2.0.1
+      estree-util-value-to-estree: 1.3.0
+      toml: 3.0.0
+      unified: 10.1.2
+      yaml: 2.1.1
+    dev: false
+
   /remark-mdx/2.1.2:
     resolution: {integrity: sha512-npQagPdczPAv0xN9F8GSi5hJfAe/z6nBjylyfOfjLOmz086ahWrIjlk4BulRfNhA+asutqWxyuT3DFVsxiTVHA==}
     dependencies:
@@ -14139,7 +14266,6 @@ packages:
   /require-directory/2.1.1:
     resolution: {integrity: sha512-fGxEI7+wsG9xrvdjsrlmL22OMTTiHRwAMroiEeMgq8gzoLC/PQr7RsRDSTLUg/bZAZtF+TVIkHc6/4RIKrui+Q==}
     engines: {node: '>=0.10.0'}
-    dev: true
 
   /require-from-string/2.0.2:
     resolution: {integrity: sha512-Xf0nWe6RseziFMu+Ap9biiUbmplq6S9/p+7w7YXP/JBHhrUDDUhwa+vANyubuqfZWTveU//DYVGsDG7RKL/vEw==}
@@ -14981,6 +15107,15 @@ packages:
       source-map-support: 0.5.21
     dev: true
 
+  /test-exclude/6.0.0:
+    resolution: {integrity: sha512-cAGWPIyOHU6zlmg88jwm7VRyXnMN7iV68OGAbYDk/Mh/xC/pzVPlQtY6ngoIH/5/tciuhGfvESU8GrHrcxD56w==}
+    engines: {node: '>=8'}
+    dependencies:
+      '@istanbuljs/schema': 0.1.3
+      glob: 7.2.3
+      minimatch: 3.1.2
+    dev: false
+
   /text-table/0.2.0:
     resolution: {integrity: sha512-N+8UisAXDGk8PFXP4HAzVR9nbfmVJ3zYLAWiTIoqC5v5isinhr+r5uaO8+7r3BMfuNIufIsA7RdpVgacC2cSpw==}
     dev: true
@@ -15019,6 +15154,10 @@ packages:
     engines: {node: '>=0.6'}
     dev: true
 
+  /toml/3.0.0:
+    resolution: {integrity: sha512-y/mWCZinnvxjTKYhJ+pYxwD0mRLVvOtdS2Awbgxln6iEnt4rk0yBxeSBHkGJcPucRiG0e55mwWp+g/05rsrd6w==}
+    dev: false
+
   /totalist/1.1.0:
     resolution: {integrity: sha512-gduQwd1rOdDMGxFG1gEvhV88Oirdo2p+KjoYFU7k2g+i7n6AFFbDQ5kMPUsW0pNbfQsB/cwXvT1i4Bue0s9g5g==}
     engines: {node: '>=6'}
@@ -15554,6 +15693,15 @@ packages:
     resolution: {integrity: sha512-l8lCEmLcLYZh4nbunNZvQCJc5pv7+RCwa8q/LdUx8u7lsWvPDKmpodJAJNwkAhJC//dFY48KuIEmjtd4RViDrA==}
     dev: true
 
+  /v8-to-istanbul/9.0.1:
+    resolution: {integrity: sha512-74Y4LqY74kLE6IFyIjPtkSTWzUZmj8tdHT9Ii/26dvQ6K9Dl2NbEfj0XgU2sHCtKgt5VupqhlO/5aWuqS+IY1w==}
+    engines: {node: '>=10.12.0'}
+    dependencies:
+      '@jridgewell/trace-mapping': 0.3.14
+      '@types/istanbul-lib-coverage': 2.0.4
+      convert-source-map: 1.8.0
+    dev: false
+
   /validate-npm-package-license/3.0.4:
     resolution: {integrity: sha512-DpKm2Ui/xN7/HQKCtpZxoRWBhZ9Z0kqtygG8XCgNQ8ZlDnxuQmWhj566j8fN4Cu3/JmbhsDo7fcAJq4s9h27Ew==}
     dependencies:
@@ -16017,7 +16165,6 @@ packages:
       ansi-styles: 4.3.0
       string-width: 4.2.3
       strip-ansi: 6.0.1
-    dev: true
 
   /wrap-ansi/8.0.1:
     resolution: {integrity: sha512-QFF+ufAqhoYHvoHdajT/Po7KoXVBPXS2bgjIam5isfWJPfIOnQZ50JtUiVvCv/sjgacf3yRrt2ZKUZ/V4itN4g==}
@@ -16046,7 +16193,6 @@ packages:
   /y18n/5.0.8:
     resolution: {integrity: sha512-0pfFzegeDWJHJIAmTLRP2DwHjdF5s7jo9tuztdQxAhINCdvS+3nGINqPd00AphqJR/0LhANUS6/+7SCb98YOfA==}
     engines: {node: '>=10'}
-    dev: true
 
   /yallist/2.1.2:
     resolution: {integrity: sha512-ncTzHV7NvsQZkYe1DW7cbDLm0YpzHmZF5r/iyP3ZnQtMiJ+pjzisCiMNI+Sj+xQF5pXhSHxSB3uDbsBTzY/c2A==}
@@ -16078,7 +16224,11 @@ packages:
   /yargs-parser/20.2.4:
     resolution: {integrity: sha512-WOkpgNhPTlE73h4VFAFsOnomJVaovO8VqLDzy5saChRBFQFBoMYirowyW+Q9HB4HFF4Z7VZTiG3iSzJJA29yRA==}
     engines: {node: '>=10'}
-    dev: true
+
+  /yargs-parser/20.2.9:
+    resolution: {integrity: sha512-y11nGElTIV+CT3Zv9t7VKl+Q3hTQoT9a1Qzezhhl6Rp21gJ/IVTW7Z3y9EWXhuUBC2Shnf+DX0antecpAwSP8w==}
+    engines: {node: '>=10'}
+    dev: false
 
   /yargs-parser/21.0.1:
     resolution: {integrity: sha512-9BK1jFpLzJROCI5TzwZL/TU4gqjK5xiHV/RfWLOahrjAko/e4DJkRDZQXfvqAsiZzzYhgAzbgz6lg48jcm4GLg==}
@@ -16122,7 +16272,6 @@ packages:
       string-width: 4.2.3
       y18n: 5.0.8
       yargs-parser: 20.2.4
-    dev: true
 
   /yargs/17.5.1:
     resolution: {integrity: sha512-t6YAJcxDkNX7NFYiVtKvWUz8l+PaKTLiL63mJYWR2GnHq2gjEWISzsLp9wg3aY36dY1j+gfIEL3pIF+XlJJfbA==}