Add dotAll polyfill (#532)

packages/remark-mdx/tag.js

@@ -3,11 +3,15 @@
 //
 // MIT License https://github.com/remarkjs/remark/blob/master/license
 
+// https://github.com/DmitrySoshnikov/babel-plugin-transform-modern-regexp#dotall-s-flag
+// Firefox and other browsers don't support the dotAll ("s") flag, but it can be polyfilled via this:
+const dotAllPolyfill = '[\0-\uFFFF]'
+
 const attributeName = '[a-zA-Z_:][a-zA-Z0-9:._-]*'
 const unquoted = '[^"\'=<>`\\u0000-\\u0020]+'
 const singleQuoted = "'[^']*'"
 const doubleQuoted = '"[^"]*"'
-const jsProps = '{.*}'
+const jsProps = '{.*}'.replace('.', dotAllPolyfill)
 const attributeValue =
   '(?:' +
   unquoted +
@@ -23,7 +27,7 @@ const attribute =
 const openTag = '<[A-Za-z]*[A-Za-z0-9\\.\\-]*' + attribute + '*\\s*\\/?>'
 const closeTag = '<\\/[A-Za-z][A-Za-z0-9\\.\\-]*\\s*>'
 const comment = '<!---->|<!--(?:-?[^>-])(?:-?[^-])*-->'
-const processing = '<[?].*?[?]>'
+const processing = '<[?].*?[?]>'.replace('.', dotAllPolyfill)
 const declaration = '<![A-Za-z]+\\s+[^>]*>'
 const cdata = '<!\\[CDATA\\[[\\s\\S]*?\\]\\]>'
 
@@ -42,6 +46,5 @@ exports.tag = new RegExp(
     declaration +
     '|' +
     cdata +
-    ')',
-  's'
+    ')'
 )