diff --git a/PExpr.cc b/PExpr.cc
index bce998419..b358542b5 100644
--- a/PExpr.cc
+++ b/PExpr.cc
@@ -126,9 +126,8 @@ PEBinary::~PEBinary()
 
 void PEBinary::declare_implicit_nets(LexicalScope*scope, NetNet::Type type)
 {
-      assert(left_ && right_);
-      left_->declare_implicit_nets(scope, type);
-      right_->declare_implicit_nets(scope, type);
+      if (left_) left_->declare_implicit_nets(scope, type);
+      if (right_) right_->declare_implicit_nets(scope, type);
 }
 
 bool PEBinary::has_aa_term(Design*des, NetScope*scope) const
diff --git a/Statement.cc b/Statement.cc
index e5f5f169e..e200f7734 100644
--- a/Statement.cc
+++ b/Statement.cc
@@ -206,8 +206,8 @@ const pform_name_t& PCallTask::path() const
       return path_;
 }
 
-PCase::PCase(NetCase::TYPE t, PExpr*ex, svector<PCase::Item*>*l)
-: type_(t), expr_(ex), items_(l)
+PCase::PCase(ivl_case_quality_t q, NetCase::TYPE t, PExpr*ex, svector<PCase::Item*>*l)
+: quality_(q), type_(t), expr_(ex), items_(l)
 {
 }
 
diff --git a/Statement.h b/Statement.h
index ae5e162b6..92791d9d2 100644
--- a/Statement.h
+++ b/Statement.h
@@ -254,7 +254,7 @@ class PCase  : public Statement {
 	    Statement*stat;
       };
 
-      PCase(NetCase::TYPE, PExpr*ex, svector<Item*>*);
+      PCase(ivl_case_quality_t, NetCase::TYPE, PExpr*ex, svector<Item*>*);
       ~PCase();
 
       virtual NetProc* elaborate(Design*des, NetScope*scope) const;
@@ -263,6 +263,7 @@ class PCase  : public Statement {
       virtual void dump(ostream&out, unsigned ind) const;
 
     private:
+      ivl_case_quality_t quality_;
       NetCase::TYPE type_;
       PExpr*expr_;
 
diff --git a/compiler.h b/compiler.h
index 6eccc8743..fd50cd52f 100644
--- a/compiler.h
+++ b/compiler.h
@@ -1,7 +1,7 @@
 #ifndef IVL_compiler_H
 #define IVL_compiler_H
 /*
- * Copyright (c) 1999-2017 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 1999-2019 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -177,9 +177,12 @@ extern bool gn_icarus_misc_flag;
    is false, then skip elaboration of specify behavior. */
 extern bool gn_specify_blocks_flag;
 
-/* If this flag is true, then elaborate assertions. If this flag is
-   false, then stub out assertion statements. */
-extern bool gn_assertions_flag;
+/* If this flag is true, then elaborate supported assertion statements. If
+   this flag is false, then stub out supported assertion statements. */
+extern bool gn_supported_assertions_flag;
+/* If this flag is true, then error on unsupported assertion statements. If
+   this flag is false, then stub out unsupported assertion statements. */
+extern bool gn_unsupported_assertions_flag;
 
 /* If this flag is true, then support/elaborate Verilog-AMS. */
 extern bool gn_verilog_ams_flag;
diff --git a/design_dump.cc b/design_dump.cc
index 88cf88bea..cf8c1d4f3 100644
--- a/design_dump.cc
+++ b/design_dump.cc
@@ -1150,15 +1150,29 @@ void NetBlock::dump(ostream&o, unsigned ind) const
 
 void NetCase::dump(ostream&o, unsigned ind) const
 {
+      o << setw(ind) << "";
+      switch (quality_) {
+	  case IVL_CASE_QUALITY_BASIC:
+	    break;
+	  case IVL_CASE_QUALITY_UNIQUE:
+	    o << "unique ";
+	    break;
+	  case IVL_CASE_QUALITY_UNIQUE0:
+	    o << "unique0 ";
+	    break;
+	  case IVL_CASE_QUALITY_PRIORITY:
+	    o << "priority ";
+	    break;
+      }
       switch (type_) {
 	  case EQ:
-	    o << setw(ind) << "" << "case (" << *expr_ << ")" << endl;
+	    o << "case (" << *expr_ << ")" << endl;
 	    break;
 	  case EQX:
-	    o << setw(ind) << "" << "casex (" << *expr_ << ")" << endl;
+	    o << "casex (" << *expr_ << ")" << endl;
 	    break;
 	  case EQZ:
-	    o << setw(ind) << "" << "casez (" << *expr_ << ")" << endl;
+	    o << "casez (" << *expr_ << ")" << endl;
 	    break;
       }
 
diff --git a/driver/iverilog.man.in b/driver/iverilog.man.in
index 2578969da..0f49fea4f 100644
--- a/driver/iverilog.man.in
+++ b/driver/iverilog.man.in
@@ -1,4 +1,4 @@
-.TH iverilog 1 "Sep 20th, 2019" "" "Version %M.%n%E"
+.TH iverilog 1 "Oct 5th, 2019" "" "Version %M.%n%E"
 .SH NAME
 iverilog - Icarus Verilog compiler
 
@@ -80,10 +80,11 @@ use any of the new \fIIEEE1800\fP keywords.
 Enable or disable (default) support for Verilog\-AMS.
 Very little Verilog\-AMS specific functionality is currently supported.
 .TP 8
-.B -gassertions\fI|\fP-gno-assertions
+.B -gassertions\fI|\fP-gsupported-assertions\fI|\fP-gno-assertions
 Enable (default) or disable SystemVerilog assertions. When enabled,
 assertion statements are elaborated. When disabled, assertion statements
-are parsed but ignored.
+are parsed but ignored. The \fB\-gsupported-assertions\fP option only
+enables assertions that are currently supported by the compiler.
 .TP 8
 .B -gspecify\fI|\fP-gno-specify
 Enable or disable (default) specify block support. When enabled,
@@ -129,7 +130,7 @@ default, parts of the expression that do not depend on the changed
 input value(s) are not re-evaluated. If an expression contains a call
 to a function that doesn't depend solely on its input values or that
 has side effects, the resulting behavior will differ from that
-required by the standard. Using \fI\-gstrict\-ca\-eval\fP will force
+required by the standard. Using \fB\-gstrict\-ca\-eval\fP will force
 standard compliant behavior (with some loss in performance).
 .TP 8
 .B -gstrict-expr-width\fI|\fP-gno-strict-expr-width
diff --git a/driver/main.c b/driver/main.c
index b723d7ff3..56228637a 100644
--- a/driver/main.c
+++ b/driver/main.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000-2017 Stephen Williams (steve@icarus.com)
+ * Copyright (c) 2000-2019 Stephen Williams (steve@icarus.com)
  *
  *    This source code is free software; you can redistribute it
  *    and/or modify it in source code form under the terms of the GNU
@@ -748,6 +748,9 @@ static int process_generation(const char*name)
       else if (strcmp(name,"assertions") == 0)
 	    gen_assertions = "assertions";
 
+      else if (strcmp(name,"supported-assertions") == 0)
+	    gen_assertions = "supported-assertions";
+
       else if (strcmp(name,"no-assertions") == 0)
 	    gen_assertions = "no-assertions";
 
@@ -804,6 +807,7 @@ static int process_generation(const char*name)
 		            "    2009    -- IEEE1800-2009\n"
 		            "    2012    -- IEEE1800-2012\n"
 		            "Other generation flags:\n"
+		            "    assertions | supported-assertions | no-assertions\n"
 		            "    specify | no-specify\n"
 		            "    verilog-ams | no-verilog-ams\n"
 		            "    std-include | no-std-include\n"
@@ -1176,7 +1180,7 @@ int main(int argc, char **argv)
 
       if (version_flag || verbose_flag) {
 	    printf("Icarus Verilog version " VERSION " (" VERSION_TAG ")\n\n");
-	    printf("Copyright 1998-2017 Stephen Williams\n\n");
+	    printf("Copyright 1998-2019 Stephen Williams\n\n");
 	    puts(NOTICE);
       }
 
diff --git a/elaborate.cc b/elaborate.cc
index 0875929f3..5af51cc64 100644
--- a/elaborate.cc
+++ b/elaborate.cc
@@ -2321,8 +2321,6 @@ NetExpr* PAssign_::elaborate_rval_(Design*des, NetScope*scope,
 
       if (!is_constant_ || !rv) return rv;
 
-      if (dynamic_cast<NetENew*>(rv)) return rv;
-
       cerr << get_fileline() << ": error: "
             "The RHS expression must be constant." << endl;
       cerr << get_fileline() << "       : "
@@ -3129,7 +3127,7 @@ NetProc* PCase::elaborate(Design*des, NetScope*scope) const
 		  icount += cur->expr.size();
       }
 
-      NetCase*res = new NetCase(type_, expr, icount);
+      NetCase*res = new NetCase(quality_, type_, expr, icount);
       res->set_line(*this);
 
 	/* Iterate over all the case items (guard/statement pairs)
diff --git a/ivl_target.h b/ivl_target.h
index 30ae0194f..f0ee992e9 100644
--- a/ivl_target.h
+++ b/ivl_target.h
@@ -434,6 +434,14 @@ typedef enum ivl_statement_type_e {
       IVL_ST_WHILE   = 23
 } ivl_statement_type_t;
 
+/* Case statements can be tagged as unique/unique0/priority. */
+typedef enum ivl_case_quality_t {
+      IVL_CASE_QUALITY_BASIC    = 0,  /* no quality flags */
+      IVL_CASE_QUALITY_UNIQUE   = 1,
+      IVL_CASE_QUALITY_UNIQUE0  = 2,
+      IVL_CASE_QUALITY_PRIORITY = 3
+} ivl_case_quality_t;
+
 /* SystemVerilog allows a system function to be called as a task. */
 typedef enum ivl_sfunc_as_task_e {
       IVL_SFUNC_AS_TASK_ERROR   = 0,
@@ -2222,6 +2230,8 @@ extern ivl_scope_t ivl_stmt_call(ivl_statement_t net);
 extern unsigned ivl_stmt_case_count(ivl_statement_t net);
   /* IVL_ST_CASE,IVL_ST_CASER,IVL_ST_CASEX,IVL_ST_CASEZ */
 extern ivl_expr_t ivl_stmt_case_expr(ivl_statement_t net, unsigned i);
+  /* IVL+ST_CASE,IVL_ST_CASER,IVL_ST_CASEX,IVL_ST_CASEZ */
+extern ivl_case_quality_t ivl_stmt_case_quality(ivl_statement_t net);
   /* IVL_ST_CASE,IVL_ST_CASER,IVL_ST_CASEX,IVL_ST_CASEZ */
 extern ivl_statement_t ivl_stmt_case_stmt(ivl_statement_t net, unsigned i);
   /* IVL_ST_CONDIT IVL_ST_CASE IVL_ST_REPEAT IVL_ST_WHILE */
diff --git a/main.cc b/main.cc
index 938100cca..60ec62e7e 100644
--- a/main.cc
+++ b/main.cc
@@ -1,5 +1,5 @@
 const char COPYRIGHT[] =
-          "Copyright (c) 1998-2017 Stephen Williams (steve@icarus.com)";
+          "Copyright (c) 1998-2019 Stephen Williams (steve@icarus.com)";
 
 /*
  *    This source code is free software; you can redistribute it
@@ -104,7 +104,8 @@ generation_t generation_flag = GN_DEFAULT;
 bool gn_icarus_misc_flag = true;
 bool gn_cadence_types_flag = true;
 bool gn_specify_blocks_flag = true;
-bool gn_assertions_flag = true;
+bool gn_supported_assertions_flag = true;
+bool gn_unsupported_assertions_flag = true;
 bool gn_io_range_error_flag = true;
 bool gn_strict_ca_eval_flag = false;
 bool gn_strict_expr_width_flag = false;
@@ -331,10 +332,16 @@ static void process_generation_flag(const char*gen)
 	    gn_specify_blocks_flag = false;
 
       } else if (strcmp(gen,"assertions") == 0) {
-	    gn_assertions_flag = true;
+	    gn_supported_assertions_flag = true;
+	    gn_unsupported_assertions_flag = true;
+
+      } else if (strcmp(gen,"supported-assertions") == 0) {
+	    gn_supported_assertions_flag = true;
+	    gn_unsupported_assertions_flag = false;
 
       } else if (strcmp(gen,"no-assertions") == 0) {
-	    gn_assertions_flag = false;
+	    gn_supported_assertions_flag = false;
+	    gn_unsupported_assertions_flag = false;
 
       } else if (strcmp(gen,"verilog-ams") == 0) {
 	    gn_verilog_ams_flag = true;
diff --git a/net_proc.cc b/net_proc.cc
index 68127445f..b82abe8f1 100644
--- a/net_proc.cc
+++ b/net_proc.cc
@@ -83,8 +83,8 @@ const NetProc* NetBlock::proc_next(const NetProc*cur) const
       return cur->next_;
 }
 
-NetCase::NetCase(NetCase::TYPE c, NetExpr*ex, unsigned cnt)
-: type_(c), expr_(ex), items_(cnt)
+NetCase::NetCase(ivl_case_quality_t q, NetCase::TYPE c, NetExpr*ex, unsigned cnt)
+: quality_(q), type_(c), expr_(ex), items_(cnt)
 {
       ivl_assert(*this, expr_);
 }
diff --git a/netlist.h b/netlist.h
index 6b85a5a2a..37ed539b7 100644
--- a/netlist.h
+++ b/netlist.h
@@ -3050,6 +3050,9 @@ class NetBlock  : public NetProc {
  * way the comparisons are performed. Also, it is likely that the
  * target may be able to optimize differently.
  *
+ * Case statements can have unique, unique0, or priority attached to
+ * them. If not otherwise adorned, it is QBASIC.
+ *
  * Case can be one of three types:
  *    EQ  -- All bits must exactly match
  *    EQZ -- z bits are don't care
@@ -3059,13 +3062,15 @@ class NetCase  : public NetProc {
 
     public:
       enum TYPE { EQ, EQX, EQZ };
-      NetCase(TYPE c, NetExpr*ex, unsigned cnt);
+
+      NetCase(ivl_case_quality_t q, TYPE c, NetExpr*ex, unsigned cnt);
       ~NetCase();
 
       void set_case(unsigned idx, NetExpr*ex, NetProc*st);
 
       void prune();
 
+      inline ivl_case_quality_t case_quality() const { return quality_; }
       TYPE type() const;
       const NetExpr*expr() const { return expr_; }
       inline unsigned nitems() const { return items_.size(); }
@@ -3097,6 +3102,7 @@ class NetCase  : public NetProc {
 			      NexusSet&nex_map, NetBus&nex_out,
 			      NetBus&enables, vector<mask_t>&bitmasks);
 
+      ivl_case_quality_t quality_;
       TYPE type_;
 
       struct Item {
diff --git a/parse.y b/parse.y
index eb10d6b72..e0152f763 100644
--- a/parse.y
+++ b/parse.y
@@ -408,6 +408,7 @@ static void current_function_set_statement(const YYLTYPE&loc, vector<Statement*>
 
       svector<PEEvent*>*event_expr;
 
+      ivl_case_quality_t case_quality;
       NetNet::Type nettype;
       PGBuiltin::Type gatetype;
       NetNet::PortType porttype;
@@ -575,6 +576,7 @@ static void current_function_set_statement(const YYLTYPE&loc, vector<Statement*>
 %type <expr>    udp_initial_expr_opt
 
 %type <text> register_variable net_variable event_variable endlabel_opt class_declaration_endlabel_opt
+%type <text> block_identifier_opt
 %type <perm_strings> register_variable_list net_variable_list event_variable_list
 %type <perm_strings> list_of_identifiers loop_variables
 %type <port_list> list_of_port_identifiers list_of_variable_port_identifiers
@@ -652,6 +654,9 @@ static void current_function_set_statement(const YYLTYPE&loc, vector<Statement*>
 %type <statement> statement statement_item statement_or_null
 %type <statement> compressed_statement
 %type <statement> loop_statement for_step jump_statement
+%type <statement> concurrent_assertion_statement
+%type <statement> deferred_immediate_assertion_statement
+%type <statement> simple_immediate_assertion_statement
 %type <statement> procedural_assertion_statement
 %type <statement_list> statement_or_null_list statement_or_null_list_opt
 
@@ -667,11 +672,14 @@ static void current_function_set_statement(const YYLTYPE&loc, vector<Statement*>
 
 %type <real_type> non_integer_type
 %type <int_val> assert_or_assume
+%type <int_val> deferred_mode
 %type <int_val> atom2_type
 %type <int_val> module_start module_end
 
 %type <lifetime> lifetime lifetime_opt
 
+%type <case_quality> unique_priority
+
 %token K_TAND
 %right K_PLUS_EQ K_MINUS_EQ K_MUL_EQ K_DIV_EQ K_MOD_EQ K_AND_EQ K_OR_EQ
 %right K_XOR_EQ K_LS_EQ K_RS_EQ K_RSS_EQ
@@ -724,6 +732,7 @@ assert_or_assume
 
 assertion_item /* IEEE1800-2012: A.6.10 */
   : concurrent_assertion_item
+  | deferred_immediate_assertion_item
   ;
 
 assignment_pattern /* IEEE1800-2005: A.6.7.1 */
@@ -744,7 +753,9 @@ assignment_pattern /* IEEE1800-2005: A.6.7.1 */
      implements it in a LALR way. */
 block_identifier_opt /* */
   : IDENTIFIER ':'
+      { $$ = $1; }
   |
+      { $$ = 0; }
   ;
 
 class_declaration /* IEEE1800-2005: A.1.2 */
@@ -988,16 +999,98 @@ class_new /* IEEE1800-2005 A.2.4 */
      concurrent_assertion_statement and checker_instantiation rules. */
 
 concurrent_assertion_item /* IEEE1800-2012 A.2.10 */
-  : block_identifier_opt K_assert K_property '(' property_spec ')' statement_or_null
-      { /* */
-	if (gn_assertions_flag) {
-	      yyerror(@2, "sorry: concurrent_assertion_item not supported."
-		      " Try -gno-assertion to turn this message off.");
-	}
+  : block_identifier_opt concurrent_assertion_statement
+      { delete $1;
+	delete $2;
       }
-  | block_identifier_opt K_assert K_property '(' error ')' statement_or_null
+  ;
+
+concurrent_assertion_statement /* IEEE1800-2012 A.2.10 */
+  : assert_or_assume K_property '(' property_spec ')' statement_or_null %prec less_than_K_else
+      { /* */
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: concurrent_assertion_item not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+        $$ = 0;
+      }
+  | assert_or_assume K_property '(' property_spec ')' K_else statement_or_null
+      { /* */
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: concurrent_assertion_item not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+        $$ = 0;
+      }
+  | assert_or_assume K_property '(' property_spec ')' statement_or_null K_else statement_or_null
+      { /* */
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: concurrent_assertion_item not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+        $$ = 0;
+      }
+  | K_cover K_property '(' property_spec ')' statement_or_null
+      { /* */
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: concurrent_assertion_item not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+        $$ = 0;
+      }
+      /* For now, cheat, and use property_spec for the sequence specification.
+         They are syntactically identical. */
+  | K_cover K_sequence '(' property_spec ')' statement_or_null
+      { /* */
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: concurrent_assertion_item not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+        $$ = 0;
+      }
+  | K_restrict K_property '(' property_spec ')' ';'
+      { /* */
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@2, "sorry: concurrent_assertion_item not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+        $$ = 0;
+      }
+  | assert_or_assume K_property '(' error ')' statement_or_null %prec less_than_K_else
       { yyerrok;
         yyerror(@2, "error: Error in property_spec of concurrent assertion item.");
+        $$ = 0;
+      }
+  | assert_or_assume K_property '(' error ')' K_else statement_or_null
+      { yyerrok;
+        yyerror(@2, "error: Error in property_spec of concurrent assertion item.");
+        $$ = 0;
+      }
+  | assert_or_assume K_property '(' error ')' statement_or_null K_else statement_or_null
+      { yyerrok;
+        yyerror(@2, "error: Error in property_spec of concurrent assertion item.");
+        $$ = 0;
+      }
+  | K_cover K_property '(' error ')' statement_or_null
+      { yyerrok;
+        yyerror(@2, "error: Error in property_spec of concurrent assertion item.");
+        $$ = 0;
+      }
+  | K_cover K_sequence '(' error ')' statement_or_null
+      { yyerrok;
+        yyerror(@2, "error: Error in property_spec of concurrent assertion item.");
+        $$ = 0;
+      }
+  | K_restrict K_property '(' error ')' ';'
+      { yyerrok;
+        yyerror(@2, "error: Error in property_spec of concurrent assertion item.");
+        $$ = 0;
       }
   ;
 
@@ -1061,6 +1154,7 @@ data_declaration /* IEEE1800-2005: A.2.1.3 */
   | attribute_list_opt K_event event_variable_list ';'
       { if ($3) pform_make_events($3, @2.text, @2.first_line);
       }
+  | attribute_list_opt package_import_declaration
   ;
 
 data_type /* IEEE1800-2005: A.2.2.1 */
@@ -1166,6 +1260,84 @@ data_type_or_implicit_or_void
       }
   ;
 
+deferred_immediate_assertion_item /* IEEE1800-2012: A.6.10 */
+  : block_identifier_opt deferred_immediate_assertion_statement
+      { delete $1;
+	delete $2;
+      }
+  ;
+
+deferred_immediate_assertion_statement /* IEEE1800-2012 A.6.10 */
+  : assert_or_assume deferred_mode '(' expression ')' statement_or_null %prec less_than_K_else
+      {
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: Deferred assertions are not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+	delete $4;
+	delete $6;
+	$$ = 0;
+      }
+  | assert_or_assume deferred_mode '(' expression ')' K_else statement_or_null
+      {
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: Deferred assertions are not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+	delete $4;
+	delete $7;
+	$$ = 0;
+      }
+  | assert_or_assume deferred_mode '(' expression ')' statement_or_null K_else statement_or_null
+      {
+	if (gn_unsupported_assertions_flag) {
+	      yyerror(@1, "sorry: Deferred assertions are not supported."
+		      " Try -gno-assertions or -gsupported-assertions"
+		      " to turn this message off.");
+	}
+	delete $4;
+	delete $6;
+	delete $8;
+	$$ = 0;
+      }
+  | K_cover deferred_mode '(' expression ')' statement_or_null
+      {
+	  /* Coverage collection is not currently supported. */
+	delete $4;
+	delete $6;
+	$$ = 0;
+      }
+  | assert_or_assume deferred_mode '(' error ')' statement_or_null %prec less_than_K_else
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $6;
+      }
+  | assert_or_assume deferred_mode '(' error ')' K_else statement_or_null
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $7;
+      }
+  | assert_or_assume deferred_mode '(' error ')' statement_or_null K_else statement_or_null
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $6;
+      }
+  | K_cover deferred_mode '(' error ')' statement_or_null
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $6;
+      }
+  ;
+
+deferred_mode
+  : '#' DEC_NUMBER
+      { if (!$2->is_zero()) {
+	      yyerror(@2, "error: Delay value must be zero for deferred assertion.");
+	}
+        delete $2;
+	$$ = 0; }
+  | K_final
+      { $$ = 1; }
+  ;
+
   /* NOTE: The "module" rule of the description combines the
      module_declaration, program_declaration, and interface_declaration
      rules from the standard description. */
@@ -1574,12 +1746,10 @@ variable_decl_assignment /* IEEE1800-2005 A.2.3 */
 	delete[]$1;
 	$$ = tmp;
       }
-  | IDENTIFIER '=' K_new '(' ')'
+  | IDENTIFIER '=' class_new
       { decl_assignment_t*tmp = new decl_assignment_t;
 	tmp->name = lex_strings.make($1);
-	PENewClass*expr = new PENewClass;
-	FILE_NAME(expr, @3);
-	tmp->expr .reset(expr);
+	tmp->expr .reset($3);
 	delete[]$1;
 	$$ = tmp;
       }
@@ -1845,65 +2015,17 @@ port_direction_opt
   |                { $$ = NetNet::PIMPLICIT; }
   ;
 
-property_expr /* IEEE1800-2012 A.2.10 */
-  : expression
+procedural_assertion_statement /* IEEE1800-2012 A.6.10 */
+  : concurrent_assertion_statement
+      { $$ = $1; }
+  | simple_immediate_assertion_statement
+      { $$ = $1; }
+  | deferred_immediate_assertion_statement
+      { $$ = $1; }
   ;
 
-procedural_assertion_statement /* IEEE1800-2012 A.6.10 */
-    // $assertcontrol is not yet supported.
-  : assert_or_assume '(' expression ')' statement_or_null %prec less_than_K_else
-      {
-	if (gn_assertions_flag) {
-	      list<PExpr*>arg_list;
-	      PCallTask*tmp1 = new PCallTask(lex_strings.make("$error"), arg_list);
-	      FILE_NAME(tmp1, @1);
-	      PCondit*tmp2 = new PCondit($3, $5, tmp1);
-	      FILE_NAME(tmp2, @1);
-	      $$ = tmp2;
-        } else {
-	      $$ = 0;
-	}
-      }
-  | assert_or_assume '(' expression ')' K_else statement_or_null
-      {
-	if (gn_assertions_flag) {
-	      PCondit*tmp = new PCondit($3, 0, $6);
-	      FILE_NAME(tmp, @1);
-	      $$ = tmp;
-        } else {
-	      $$ = 0;
-	}
-      }
-  | assert_or_assume '(' expression ')' statement_or_null K_else statement_or_null
-      {
-	if (gn_assertions_flag) {
-	      PCondit*tmp = new PCondit($3, $5, $7);
-	      FILE_NAME(tmp, @1);
-	      $$ = tmp;
-        } else {
-	      $$ = 0;
-	}
-      }
-  | K_cover '(' expression ')' statement_or_null
-      // Coverage collection is not currently supported.
-      { $$ = 0; }
-
-  | assert_or_assume '(' error ')' statement_or_null %prec less_than_K_else
-      { yyerror(@1, "error: Malformed conditional expression.");
-	$$ = $5;
-      }
-  | assert_or_assume '(' error ')' K_else statement_or_null
-      { yyerror(@1, "error: Malformed conditional expression.");
-	$$ = $6;
-      }
-  | assert_or_assume '(' error ')' statement_or_null K_else statement_or_null
-      { yyerror(@1, "error: Malformed conditional expression.");
-	$$ = $5;
-      }
-  | K_cover '(' error ')' statement_or_null
-      { yyerror(@1, "error: Malformed conditional expression.");
-	$$ = $5;
-      }
+property_expr /* IEEE1800-2012 A.2.10 */
+  : expression
   ;
 
   /* The property_qualifier rule is as literally described in the LRM,
@@ -1956,6 +2078,72 @@ signing /* IEEE1800-2005: A.2.2.1 */
   | K_unsigned { $$ = false; }
   ;
 
+simple_immediate_assertion_statement /* IEEE1800-2012 A.6.10 */
+  : assert_or_assume '(' expression ')' statement_or_null %prec less_than_K_else
+      {
+	if (gn_supported_assertions_flag) {
+	      list<PExpr*>arg_list;
+	      PCallTask*tmp1 = new PCallTask(lex_strings.make("$error"), arg_list);
+	      FILE_NAME(tmp1, @1);
+	      PCondit*tmp2 = new PCondit($3, $5, tmp1);
+	      FILE_NAME(tmp2, @1);
+	      $$ = tmp2;
+	} else {
+	      delete $3;
+	      delete $5;
+	      $$ = 0;
+	}
+      }
+  | assert_or_assume '(' expression ')' K_else statement_or_null
+      {
+	if (gn_supported_assertions_flag) {
+	      PCondit*tmp = new PCondit($3, 0, $6);
+	      FILE_NAME(tmp, @1);
+	      $$ = tmp;
+	} else {
+	      delete $3;
+	      delete $6;
+	      $$ = 0;
+	}
+      }
+  | assert_or_assume '(' expression ')' statement_or_null K_else statement_or_null
+      {
+	if (gn_supported_assertions_flag) {
+	      PCondit*tmp = new PCondit($3, $5, $7);
+	      FILE_NAME(tmp, @1);
+	      $$ = tmp;
+	} else {
+	      delete $3;
+	      delete $5;
+	      delete $7;
+	      $$ = 0;
+	}
+      }
+  | K_cover '(' expression ')' statement_or_null
+      {
+	  /* Coverage collection is not currently supported. */
+	delete $3;
+	delete $5;
+	$$ = 0;
+      }
+  | assert_or_assume '(' error ')' statement_or_null %prec less_than_K_else
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $5;
+      }
+  | assert_or_assume '(' error ')' K_else statement_or_null
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $6;
+      }
+  | assert_or_assume '(' error ')' statement_or_null K_else statement_or_null
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $5;
+      }
+  | K_cover '(' error ')' statement_or_null
+      { yyerror(@1, "error: Malformed conditional expression.");
+	$$ = $5;
+      }
+  ;
+
 simple_type_or_string /* IEEE1800-2005: A.2.2.1 */
   : integer_vector_type
       { ivl_variable_type_t use_vtype = $1;
@@ -6433,27 +6621,28 @@ statement_item /* This is roughly statement_item in the LRM */
 
   | jump_statement { $$ = $1; }
 
-	| K_case '(' expression ')' case_items K_endcase
-		{ PCase*tmp = new PCase(NetCase::EQ, $3, $5);
-		  FILE_NAME(tmp, @1);
-		  $$ = tmp;
-		}
-	| K_casex '(' expression ')' case_items K_endcase
-		{ PCase*tmp = new PCase(NetCase::EQX, $3, $5);
-		  FILE_NAME(tmp, @1);
-		  $$ = tmp;
-		}
-	| K_casez '(' expression ')' case_items K_endcase
-		{ PCase*tmp = new PCase(NetCase::EQZ, $3, $5);
-		  FILE_NAME(tmp, @1);
-		  $$ = tmp;
-		}
-	| K_case '(' expression ')' error K_endcase
-		{ yyerrok; }
-	| K_casex '(' expression ')' error K_endcase
-		{ yyerrok; }
-	| K_casez '(' expression ')' error K_endcase
-		{ yyerrok; }
+  | unique_priority K_case '(' expression ')' case_items K_endcase
+      { PCase*tmp = new PCase($1, NetCase::EQ, $4, $6);
+	FILE_NAME(tmp, @2);
+	$$ = tmp;
+      }
+  | unique_priority K_casex '(' expression ')' case_items K_endcase
+      { PCase*tmp = new PCase($1, NetCase::EQX, $4, $6);
+	FILE_NAME(tmp, @2);
+	$$ = tmp;
+      }
+  | unique_priority K_casez '(' expression ')' case_items K_endcase
+      { PCase*tmp = new PCase($1, NetCase::EQZ, $4, $6);
+	FILE_NAME(tmp, @1);
+	$$ = tmp;
+      }
+  | unique_priority K_case '(' expression ')' error K_endcase
+      { yyerrok; }
+  | unique_priority K_casex '(' expression ')' error K_endcase
+      { yyerrok; }
+  | unique_priority K_casez '(' expression ')' error K_endcase
+      { yyerrok; }
+
 	| K_if '(' expression ')' statement_or_null %prec less_than_K_else
 		{ PCondit*tmp = new PCondit($3, $5, 0);
 		  FILE_NAME(tmp, @1);
@@ -7108,6 +7297,13 @@ udp_primitive
 		}
 	;
 
+unique_priority
+  :             { $$ = IVL_CASE_QUALITY_BASIC; }
+  | K_unique    { $$ = IVL_CASE_QUALITY_UNIQUE; }
+  | K_unique0   { $$ = IVL_CASE_QUALITY_UNIQUE0; }
+  | K_priority  { $$ = IVL_CASE_QUALITY_PRIORITY; }
+  ;
+
   /* Many keywords can be optional in the syntax, although their
      presence is significant. This is a fairly common pattern so
      collect those rules here. */
diff --git a/pform.cc b/pform.cc
index c8a42bb17..18b391f50 100644
--- a/pform.cc
+++ b/pform.cc
@@ -2356,7 +2356,22 @@ void pform_make_modgates(const struct vlltype&loc,
 			 svector<lgate>*gates,
 			 std::list<named_pexpr_t>*attr)
 {
+	// The grammer should not allow module gates to happen outside
+	// an active module. But if really bad input errors combine in
+	// an ugly way with error recovery, then catch this
+	// implausible situation and return an error.
+      if (pform_cur_module.empty()) {
+	    cerr << loc << ": internal error: "
+		 << "Module instantiations outside module scope are not possible."
+		 << endl;
+	    error_count += 1;
+	    delete gates;
+	    return;
+      }
       assert(! pform_cur_module.empty());
+
+	// Detect some more realistic errors.
+
       if (pform_cur_module.front()->program_block) {
 	    cerr << loc << ": error: Module instantiations are not allowed in "
 		 << "program blocks." << endl;
@@ -2492,7 +2507,7 @@ void pform_make_var_init(const struct vlltype&li,
 
       PEIdent*lval = new PEIdent(name);
       FILE_NAME(lval, li);
-      PAssign*ass = new PAssign(lval, expr, true);
+      PAssign*ass = new PAssign(lval, expr, !gn_system_verilog());
       FILE_NAME(ass, li);
 
       lexical_scope->var_inits.push_back(ass);
diff --git a/pform_dump.cc b/pform_dump.cc
index 97a6f13af..099271d0c 100644
--- a/pform_dump.cc
+++ b/pform_dump.cc
@@ -840,6 +840,19 @@ void PCallTask::dump(ostream&out, unsigned ind) const
 void PCase::dump(ostream&out, unsigned ind) const
 {
       out << setw(ind) << "";
+      switch (quality_) {
+	  case IVL_CASE_QUALITY_BASIC:
+	    break;
+	  case IVL_CASE_QUALITY_UNIQUE:
+	    out << "unique ";
+	    break;
+	  case IVL_CASE_QUALITY_UNIQUE0:
+	    out << "unique0 ";
+	    break;
+	  case IVL_CASE_QUALITY_PRIORITY:
+	    out << "priority ";
+	    break;
+      }
       switch (type_) {
 	  case NetCase::EQ:
 	    out << "case";
diff --git a/t-dll-api.cc b/t-dll-api.cc
index 89b0a5aa2..12b829cca 100644
--- a/t-dll-api.cc
+++ b/t-dll-api.cc
@@ -2728,6 +2728,22 @@ extern "C" ivl_expr_t ivl_stmt_case_expr(ivl_statement_t net, unsigned idx)
       }
 }
 
+extern "C" ivl_case_quality_t ivl_stmt_case_quality(ivl_statement_t net)
+{
+      assert(net);
+      switch (net->type_) {
+	  case IVL_ST_CASE:
+	  case IVL_ST_CASER:
+	  case IVL_ST_CASEX:
+	  case IVL_ST_CASEZ:
+	    return net->u_.case_.quality;
+
+	  default:
+	    assert(0);
+	    return IVL_CASE_QUALITY_BASIC;
+      }
+}
+
 extern "C" ivl_statement_t ivl_stmt_case_stmt(ivl_statement_t net, unsigned idx)
 {
       assert(net);
diff --git a/t-dll-proc.cc b/t-dll-proc.cc
index ba0d4b1a0..ca61064e3 100644
--- a/t-dll-proc.cc
+++ b/t-dll-proc.cc
@@ -497,6 +497,7 @@ void dll_target::proc_case(const NetCase*net)
       }
       assert(stmt_cur_->type_ != IVL_ST_NONE);
 
+      stmt_cur_->u_.case_.quality = net->case_quality();
       assert(expr_ == 0);
       assert(net->expr());
       net->expr()->expr_scan(this);
diff --git a/t-dll.h b/t-dll.h
index 879a5c966..98d041e00 100644
--- a/t-dll.h
+++ b/t-dll.h
@@ -810,6 +810,7 @@ struct ivl_statement_s {
 	    } block_;
 
 	    struct { /* IVL_ST_CASE, IVL_ST_CASEX, IVL_ST_CASEZ */
+		  ivl_case_quality_t quality;
 		  ivl_expr_t cond;
 		  unsigned ncase;
 		  ivl_expr_t*case_ex;
diff --git a/tgt-stub/statement.c b/tgt-stub/statement.c
index 4eb8037a2..d52d8db4d 100644
--- a/tgt-stub/statement.c
+++ b/tgt-stub/statement.c
@@ -375,8 +375,24 @@ void show_statement(ivl_statement_t net, unsigned ind)
 	  case IVL_ST_CASEZ:
 	  case IVL_ST_CASER:
 	  case IVL_ST_CASE: {
+		ivl_case_quality_t qual = ivl_stmt_case_quality(net);
 		unsigned cnt = ivl_stmt_case_count(net);
-		fprintf(out, "%*scase (...) <%u cases>\n", ind, "", cnt);
+		const char*qual_txt = "";
+		switch (qual) {
+		    case IVL_CASE_QUALITY_BASIC:
+		      qual_txt = "basic";
+		      break;
+		    case IVL_CASE_QUALITY_UNIQUE:
+		      qual_txt = "unique";
+		      break;
+		    case IVL_CASE_QUALITY_UNIQUE0:
+		      qual_txt = "unique0";
+		      break;
+		    case IVL_CASE_QUALITY_PRIORITY:
+		      qual_txt = "priority";
+		      break;
+		}
+		fprintf(out, "%*scase (...) <%u cases, %s>\n", ind, "", cnt, qual_txt);
 		show_expression(ivl_stmt_cond_expr(net), ind+4);
 
 		for (idx = 0 ;  idx < cnt ;  idx += 1) {
diff --git a/tgt-vvp/stmt_assign.c b/tgt-vvp/stmt_assign.c
index 889371ee7..b99bd6797 100644
--- a/tgt-vvp/stmt_assign.c
+++ b/tgt-vvp/stmt_assign.c
@@ -1084,8 +1084,9 @@ static int show_stmt_assign_sig_cobject(ivl_statement_t net)
 	    ivl_type_t prop_type = ivl_type_prop_type(sig_type, prop_idx);
 
 	    if (ivl_type_base(prop_type) == IVL_VT_BOOL) {
-		  assert(ivl_type_packed_dimensions(prop_type) == 1);
-		  assert(ivl_type_packed_msb(prop_type,0) >= ivl_type_packed_lsb(prop_type, 0));
+		  assert(ivl_type_packed_dimensions(prop_type) == 0 ||
+		         (ivl_type_packed_dimensions(prop_type) == 1 &&
+		          ivl_type_packed_msb(prop_type,0) >= ivl_type_packed_lsb(prop_type, 0)));
 
 		  draw_eval_vec4(rval);
 		  if (ivl_expr_value(rval)!=IVL_VT_BOOL)
@@ -1097,8 +1098,9 @@ static int show_stmt_assign_sig_cobject(ivl_statement_t net)
 		  fprintf(vvp_out, "    %%pop/obj 1, 0;\n");
 
 	    } else if (ivl_type_base(prop_type) == IVL_VT_LOGIC) {
-		  assert(ivl_type_packed_dimensions(prop_type) == 1);
-		  assert(ivl_type_packed_msb(prop_type,0) >= ivl_type_packed_lsb(prop_type, 0));
+		  assert(ivl_type_packed_dimensions(prop_type) == 0 ||
+		         (ivl_type_packed_dimensions(prop_type) == 1 &&
+		          ivl_type_packed_msb(prop_type,0) >= ivl_type_packed_lsb(prop_type, 0)));
 
 		  draw_eval_vec4(rval);
 
diff --git a/tgt-vvp/vvp_process.c b/tgt-vvp/vvp_process.c
index 407df5219..fb1f22400 100644
--- a/tgt-vvp/vvp_process.c
+++ b/tgt-vvp/vvp_process.c
@@ -644,6 +644,7 @@ static int show_stmt_block_named(ivl_statement_t net, ivl_scope_t scope)
 static int show_stmt_case(ivl_statement_t net, ivl_scope_t sscope)
 {
       int rc = 0;
+      ivl_case_quality_t qual = ivl_stmt_case_quality(net);
       ivl_expr_t expr = ivl_stmt_cond_expr(net);
       unsigned count = ivl_stmt_case_count(net);
 
@@ -651,6 +652,12 @@ static int show_stmt_case(ivl_statement_t net, ivl_scope_t sscope)
 
       unsigned idx, default_case;
 
+      if (qual != IVL_CASE_QUALITY_BASIC) {
+	    fprintf(stderr, "%s:%u: tgt-vvp sorry: "
+		    "Case unique/unique0/priority qualities are ignored.\n",
+		    ivl_stmt_file(net), ivl_stmt_lineno(net));
+      }
+
       show_stmt_file_line(net, "Case statement.");
 
       local_count += count + 1;