Flag x: Clean up token separators in more cases

README.md

@@ -163,15 +163,17 @@ The following example illustrates how subroutines and backreferences differ:
 ```js
 // A backreference with \k<name>
 regex`(?<prefix>sens|respons)e\ and\ \k<prefix>ibility`
-/* Matches: - 'sense and sensibility'
-            - 'response and responsibility' */
+/* Matches:
+- 'sense and sensibility'
+- 'response and responsibility' */
 
 // A subroutine with \g<name>
 regex`(?<prefix>sens|respons)e\ and\ \g<prefix>ibility`
-/* Matches: - 'sense and sensibility'
-            - 'sense and responsibility'
-            - 'response and sensibility'
-            - 'response and responsibility' */
+/* Matches:
+- 'sense and sensibility'
+- 'sense and responsibility'
+- 'response and sensibility'
+- 'response and responsibility' */
 ```
 
 Subroutines go beyond the composition benefits of [interpolation](#-interpolation). Apart from the obvious difference that they don't require variables to be defined outside of the regex, they also don't simply insert the referenced subpattern.

spec/flag-x-spec.js

@@ -102,6 +102,10 @@ describe('flag x', () => {
       expect(() => regex`(?< n >)`).toThrow();
       expect(() => regex`(?<n>)\k< n >`).toThrow();
     });
+
+    it('should avoid adding token separators when it is safe to do so', () => {
+      expect(regex` ^ (?! a \s b . c | d [] e ) $ `.source).toBe('^(?!a\\sb.c|d[]e)$');
+    });
   });
 
   describe('in character class context', () => {

src/flag-x.js

@@ -139,11 +139,11 @@ export function rakePostprocessor(expression) {
   // No need for separators at:
   // - The beginning, if not followed by a quantifier.
   // - The end.
-  // - Before one of `()|$\`.
-  // - After one of `()|>^`, `(?:`, or a lookaround opening.
+  // - Before one of `()|.[$\`.
+  // - After one of `()|.]^>`, `\[bBdDfnrsStvwW]`, `(?:`, or a lookaround opening.
   expression = replaceUnescaped(
     expression,
-    String.raw`^${sep}(?![?*+{])|${sep}$|${sep}(?=[()|$\\])|(?<=[()|>^]|\(\?(?:[:=!]|<[=!]))${sep}`,
+    String.raw`^${sep}(?![?*+{])|${sep}$|${sep}(?=[()|.[$\\])|(?<=[()|.\]^>]|\\[bBdDfnrsStvwW]|\(\?(?:[:=!]|<[=!]))${sep}`,
     '',
     Context.DEFAULT
   );