[DOCS] Document TypoScript parse edge case behavior

The TypoScript parser matches valid operators
first before dealing with values.
Therefore, the TS `foo =<something` is now
considered a reference and not an assignment.

Resolves: #102101
Releases: main, 12.4
Change-Id: I7014b92f7a9120d0e77d264e964adef9d062070c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/81357
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/core/Documentation/Changelog/12.0/Breaking-97816-TypoScriptSyntaxChanges.rst

@@ -261,4 +261,29 @@ used "\\r" as single linebreak character. This old linebreak type is no longer d
 when parsing TypoScript and may lead to funny results, but chances are very low any
 instance is affected by this.
 
+Operator matching has higher precedence
+---------------------------------------
+
+The new parser looks for valid operators first, then parses things behind it.
+Consider this example:
+
+..  code-block:: typoscript
+
+    lib.nav.wrap =<ul id="nav">|</ul>
+
+This is ambiguous: The above :typoscript:`=<ul` could be interpreted both as an
+assignment :typoscript:`=` of the value :typoscript:`<ul`, or as a reference
+:typoscript:`=<` to the identifier :typoscript:`ul`.
+
+While the old parser interpreted this as an assignment, the new parser treats it
+as a reference.
+
+The above example aims for an assignment, though, which can be achieved by adding
+a whitespace between :typoscript:`=` and :typoscript:`<`:
+
+..  code-block:: typoscript
+
+    lib.nav.wrap = <ul id="nav">|</ul>
+
+
 .. index:: Backend, Frontend, TSConfig, TypoScript, NotScanned, ext:core

typo3/sysext/core/Tests/Unit/TypoScript/Tokenizer/TokenizerInterfaceTest.php

@@ -387,7 +387,7 @@ public static function tokenizeStringDataProvider(): array
                             )
                     ),
             ],
-            'identifier, assignment, value with whitespaces' => [
+            'identifier, assignment, whitespace, value' => [
                 'foo = bar',
                 (new LineStream())
                     ->append(
@@ -422,6 +422,41 @@ public static function tokenizeStringDataProvider(): array
                             )
                     ),
             ],
+            'identifier, assignment, whitespace, value with < is considered an assignment line, not a reference' => [
+                'foo = <bar',
+                (new LineStream())
+                    ->append(
+                        (new IdentifierAssignmentLine())
+                            ->setTokenStream(
+                                (new TokenStream())
+                                    ->append(new IdentifierToken(TokenType::T_IDENTIFIER, 'foo', 0, 0))
+                                    ->append(new Token(TokenType::T_BLANK, ' ', 0, 3))
+                                    ->append(new Token(TokenType::T_OPERATOR_ASSIGNMENT, '=', 0, 4))
+                                    ->append(new Token(TokenType::T_BLANK, ' ', 0, 5))
+                                    ->append(new Token(TokenType::T_VALUE, '<bar', 0, 6)),
+                            )
+                            ->setIdentifierTokenStream(
+                                (new IdentifierTokenStream())
+                                    ->append(new IdentifierToken(TokenType::T_IDENTIFIER, 'foo', 0, 0))
+                            )
+                            ->setValueTokenStream(
+                                (new TokenStream())
+                                    ->append(new Token(TokenType::T_VALUE, '<bar', 0, 6))
+                            )
+                    ),
+                (new LineStream())
+                    ->append(
+                        (new IdentifierAssignmentLine())
+                            ->setIdentifierTokenStream(
+                                (new IdentifierTokenStream())
+                                    ->append(new IdentifierToken(TokenType::T_IDENTIFIER, 'foo'))
+                            )
+                            ->setValueTokenStream(
+                                (new TokenStream())
+                                    ->append(new Token(TokenType::T_VALUE, '<bar'))
+                            )
+                    ),
+            ],
             'identifier with colon, assignment, value with whitespaces' => [
                 'foo:bar = fooValue',
                 (new LineStream())
@@ -1731,7 +1766,7 @@ public static function tokenizeStringDataProvider(): array
                             )
                     ),
             ],
-            'identifier, reference, identifiers with whitespaces' => [
+            'identifier, reference, whitespace, identifiers' => [
                 'foo =< bar1.bar2',
                 (new LineStream())
                     ->append(
@@ -1770,7 +1805,7 @@ public static function tokenizeStringDataProvider(): array
                             )
                     ),
             ],
-            'identifier, reference, relative identifiers with whitespaces' => [
+            'identifier, reference, whitespace, relative identifiers' => [
                 'foo =< .bar1.bar2',
                 (new LineStream())
                     ->append(