================================================================================
Declaration
================================================================================
attribute a : t;
--------------------------------------------------------------------------------

(design_file
  (attribute_declaration
    (identifier)
    (type_mark
      (simple_name))))

================================================================================
Specification
================================================================================
attribute attr of e : entity is expr;
--------------------------------------------------------------------------------

(design_file
  (attribute_specification
    (simple_name)
    (entity_specification
      (entity_name_list
        (entity_designator
          (simple_name)))
      (entity_class))
    (expression
      (simple_name))))

================================================================================
Specification [LRM] I
================================================================================
attribute LOCATION of ADDER1 : label is (10,15);
--------------------------------------------------------------------------------

(design_file
  (attribute_specification
    (simple_name)
    (entity_specification
      (entity_name_list
        (entity_designator
          (simple_name)))
      (entity_class))
    (expression
      (aggregate
        (positional_element_association
          (expression
            (integer_decimal)))
        (positional_element_association
          (expression
            (integer_decimal)))))))

================================================================================
Specification [LRM] II
================================================================================
attribute IMPLEMENTATION of G1: group is "74LS152";
--------------------------------------------------------------------------------

(design_file
  (attribute_specification
    (simple_name)
    (entity_specification
      (entity_name_list
        (entity_designator
          (simple_name)))
      (entity_class))
    (expression
      (string_literal))))

================================================================================
Specification [LRM] III
================================================================================
attribute CAPACITANCE of all: signal is 15 pF;
--------------------------------------------------------------------------------

(design_file
  (attribute_specification
    name: (simple_name)
    (entity_specification
      (entity_name_list
        (all))
      (entity_class))
    (expression
      (physical_literal
        (integer_decimal)
        unit: (simple_name)))))

================================================================================
Xilinx Attribute I
================================================================================
attribute ASYNC_REG : string;
attribute ASYNC_REG of sync_regs : signal is "TRUE";
attribute ASYNC_REG : boolean;
attribute ASYNC_REG of sync_regs : signal is true;
--------------------------------------------------------------------------------

(design_file
  (attribute_declaration
    (identifier)
    (type_mark
      (simple_name)))
  (attribute_specification
    (simple_name)
    (entity_specification
      (entity_name_list
        (entity_designator
          (simple_name)))
      (entity_class))
    (expression
      (string_literal)))
  (attribute_declaration
    (identifier)
    (type_mark
      (simple_name)))
  (attribute_specification
    (simple_name)
    (entity_specification
      (entity_name_list
        (entity_designator
          (simple_name)))
      (entity_class))
    (expression
      (simple_name))))
