minor symfony#19074 [Expression Language] Number of backslashes to escape a backslash (devojifr)

This PR was merged into the 5.4 branch.

Discussion
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[Expression Language] Number of backslashes to escape a backslash

To escape a backslash in a string, we must use 3 backslashes before the backslash itself.
The documentation points out we need to escape by 4 backslashes the backslash. It could be confusing, the total would 5 backslashes.

Commits
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a67b566 [Expression Language] Clarify number of backslashes to escape a backslash

Author: xabbuh

reference/formats/expression_language.rst

@@ -20,8 +20,8 @@ The component supports:
 
 .. caution::
 
-    A backslash (``\``) must be escaped by 4 backslashes (``\\\\``) in a string
-    and 8 backslashes (``\\\\\\\\``) in a regex::
+    A backslash (``\``) must be escaped by 3 backslashes (``\\\\``) in a string
+    and 7 backslashes (``\\\\\\\\``) in a regex::
 
         echo $expressionLanguage->evaluate('"\\\\"'); // prints \
         $expressionLanguage->evaluate('"a\\\\b" matches "/^a\\\\\\\\b$/"'); // returns true