[parsing] Clarify a comment.

src/parsing/pattern-rewriter.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/ast/ast.h"
 #include "src/messages.h"
 #include "src/objects-inl.h"
 #include "src/parsing/parameter-initializer-rewriter.h"
 #include "src/parsing/parser.h"
 
@@ skipping 209 matching lines @@
     // But for var declarations we need to do a new lookup.
     if (descriptor_->mode == VAR) {
       proxy = var_init_scope->NewUnresolved(factory(), name);
       // TODO(neis): Set is_assigned on proxy.
     } else {
       DCHECK_NOT_NULL(proxy);
       DCHECK_NOT_NULL(proxy->var());
       if (var_init_scope->is_script_scope() ||
           var_init_scope->is_module_scope()) {
         // We have to pessimistically assume that top-level variables will be
-        // assigned.  This is because there may be lazily parsed top-level
-        // functions, which, for efficiency, we preparse without variable
-        // tracking.
+        // assigned.  This is because they might be accessed by a lazily parsed
+        // top-level function, which, for efficiency, we preparse without
+        // variable tracking.  In the case of a script (not a module), they
+        // might also get accessed by another script.
         proxy->set_is_assigned();
       }
     }
     // Add break location for destructured sub-pattern.
     int pos = IsSubPattern() ? pattern->position() : value->position();
     Assignment* assignment =
         factory()->NewAssignment(Token::INIT, proxy, value, pos);
     block_->statements()->Add(
         factory()->NewExpressionStatement(assignment, pos), zone());
   }
@@ skipping 500 matching lines @@
 NOT_A_PATTERN(TryFinallyStatement)
 NOT_A_PATTERN(UnaryOperation)
 NOT_A_PATTERN(VariableDeclaration)
 NOT_A_PATTERN(WhileStatement)
 NOT_A_PATTERN(WithStatement)
 NOT_A_PATTERN(Yield)
 
 #undef NOT_A_PATTERN
 }  // namespace internal
 }  // namespace v8