*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/css/CSSGrammar.y

 %{
 
 /*
  *  Copyright (C) 2002-2003 Lars Knoll (knoll@kde.org)
  *  Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  *  Copyright (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *  Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  *  Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
  *  This library is free software; you can redistribute it and/or
@@ skipping 177 matching lines @@
 %token INTERNAL_DECLS_SYM
 %token INTERNAL_MEDIALIST_SYM
 %token INTERNAL_RULE_SYM
 %token INTERNAL_SELECTOR_SYM
 %token INTERNAL_VALUE_SYM
 %token INTERNAL_KEYFRAME_RULE_SYM
 %token INTERNAL_KEYFRAME_KEY_LIST_SYM
 %token INTERNAL_SUPPORTS_CONDITION_SYM
 %token KEYFRAMES_SYM
 %token WEBKIT_KEYFRAMES_SYM
-%token WEBKIT_REGION_RULE_SYM
 %token <marginBox> TOPLEFTCORNER_SYM
 %token <marginBox> TOPLEFT_SYM
 %token <marginBox> TOPCENTER_SYM
 %token <marginBox> TOPRIGHT_SYM
 %token <marginBox> TOPRIGHTCORNER_SYM
 %token <marginBox> BOTTOMLEFTCORNER_SYM
 %token <marginBox> BOTTOMLEFT_SYM
 %token <marginBox> BOTTOMCENTER_SYM
 %token <marginBox> BOTTOMRIGHT_SYM
 %token <marginBox> BOTTOMRIGHTCORNER_SYM
@@ skipping 72 matching lines @@
 %type <rule> import
 %type <rule> namespace
 %type <rule> page
 %type <rule> margin_box
 %type <rule> font_face
 %type <rule> keyframes
 %type <rule> rule
 %type <rule> valid_rule
 %type <ruleList> block_rule_body
 %type <ruleList> block_rule_list
-%type <ruleList> region_block_rule_body
-%type <ruleList> region_block_rule_list
 %type <rule> block_rule
 %type <rule> block_valid_rule
-%type <rule> region_block_rule
-%type <rule> region_block_valid_rule
-%type <rule> region
 %type <rule> supports
 %type <rule> viewport
 %type <boolean> keyframes_rule_start
 
 %type <string> maybe_ns_prefix
 
 %type <string> namespace_selector
 
 %type <string> string_or_uri
 %type <string> ident_or_string
@@ skipping 27 matching lines @@
 
 %type <id> property
 
 %type <selector> specifier
 %type <selector> specifier_list
 %type <selector> simple_selector
 %type <selector> selector
 %type <selector> relative_selector
 %type <selectorList> selector_list
 %type <selectorList> simple_selector_list
-%type <selectorList> region_selector
 %type <selector> class
 %type <selector> attrib
 %type <selector> pseudo
 %type <selector> pseudo_page
 %type <selector> page_selector
 
 %type <boolean> declaration_list
 %type <boolean> decl_list
 %type <boolean> declaration
 %type <boolean> declarations_and_margins
@@ skipping 149 matching lines @@
  ;
 
 valid_rule:
     ruleset
   | media
   | page
   | font_face
   | keyframes
   | namespace
   | import
-  | region
   | supports
   | viewport
   ;
 
 before_rule:
     /* empty */ {
         parser->startRule();
     }
   ;
 
@@ skipping 14 matching lines @@
   | block_rule_list block_rule_recovery
     ;
 
 block_rule_list:
     /* empty */ { $$ = 0; }
   | block_rule_list block_rule maybe_sgml {
       $$ = parser->appendRule($1, $2);
     }
     ;
 
-region_block_rule_body:
-    region_block_rule_list
-  | region_block_rule_list block_rule_recovery
-    ;
-
-region_block_rule_list:
-    /* empty */ { $$ = 0; }
-  | region_block_rule_list region_block_rule maybe_sgml {
-        $$ = parser->appendRule($1, $2);
-    }
-  ;
-
-region_block_rule:
-    before_rule region_block_valid_rule {
-        $$ = $2;
-        parser->endRule(!!$$);
-    }
-  | before_rule invalid_rule {
-        $$ = 0;
-        parser->endRule(false);
-    }
-  ;
-
 block_rule_recovery:
     before_rule invalid_rule_header {
         parser->endRule(false);
     }
   ;
 
-region_block_valid_rule:
-    ruleset
-  | page
-  | font_face
-  | media
-  | keyframes
-  | supports
-  | viewport
-  ;
-
 block_valid_rule:
     ruleset
   | page
   | font_face
   | media
   | keyframes
   | supports
   | viewport
   | namespace
-  | region
   ;
 
 block_rule:
     before_rule block_valid_rule {
         $$ = $2;
         parser->endRule(!!$$);
     }
   | before_rule invalid_rule {
         $$ = 0;
         parser->endRule(false);
@@ skipping 471 matching lines @@
     ;
 
 viewport:
     before_viewport_rule VIEWPORT_RULE_SYM at_rule_header_end_maybe_space
     '{' at_rule_body_start maybe_space_before_declaration declaration_list closing_brace {
         $$ = parser->createViewportRule();
         parser->markViewportRuleBodyEnd();
     }
 ;
 
-region_selector:
-    selector_list {
-        parser->setReusableRegionSelectorVector($1);
-        $$ = parser->reusableRegionSelectorVector();
-    }
-;
-
-before_region_rule:
-    /* empty */ {
-        parser->startRuleHeader(CSSRuleSourceData::REGION_RULE);
-    }
-    ;
-
-region:
-    before_region_rule WEBKIT_REGION_RULE_SYM maybe_space region_selector at_rule_header_end '{' at_rule_body_start maybe_space region_block_rule_body closing_brace {
-        $$ = parser->createRegionRule($4, $9);
-    }
-;
-
 combinator:
     '+' maybe_space { $$ = CSSSelector::DirectAdjacent; }
     | '~' maybe_space { $$ = CSSSelector::IndirectAdjacent; }
     | '>' maybe_space { $$ = CSSSelector::Child; }
     | '^' maybe_space {
         if (!RuntimeEnabledFeatures::shadowDOMEnabled())
             YYERROR;
         $$ = CSSSelector::ChildTree;
     }
     | '^' '^' maybe_space {
@@ skipping 790 matching lines @@
   | before_font_face_rule FONT_FACE_SYM at_rule_header_recovery
   | before_supports_rule SUPPORTS_SYM error error_location rule_error_recovery {
         parser->reportError($4, InvalidSupportsConditionCSSError);
         parser->popSupportsRuleData();
     }
   | before_viewport_rule VIEWPORT_RULE_SYM at_rule_header_recovery {
         parser->markViewportRuleBodyEnd();
     }
   | import_rule_start at_rule_header_recovery
   | NAMESPACE_SYM at_rule_header_recovery
-  | before_region_rule WEBKIT_REGION_RULE_SYM at_rule_header_recovery
   | error_location invalid_at at_rule_header_recovery {
         parser->resumeErrorLogging();
         parser->reportError($1, InvalidRuleCSSError);
     }
   ;
 
 invalid_rule:
     error error_location rule_error_recovery at_invalid_rule_header_end invalid_block {
         parser->reportError($2, InvalidRuleCSSError);
     }
@@ skipping 53 matching lines @@
 
 rule_error_recovery:
     /* empty */
   | rule_error_recovery error
   | rule_error_recovery invalid_square_brackets_block
   | rule_error_recovery invalid_parentheses_block
     ;
 
 %%