====== Abstract literals ======
===== Definition =====
==== abstract_literal ====
  * decimal_literal
  * based_literal

==== decimal_literal ====
  integer [ . integer ] [ exponent ]

==== based_literal ====
  base # based_integer [ . based_integer ] # [ exponent ]

==== base ====
  * integer

==== based_integer ====
  extended_digit { [ underline ] extended_digit }

==== extended_digit ====
  * digit
  * letter

==== exponent ====
<code>E [ + ] integer</code>
<code>E -integer</code>

==== integer ====
  digit { [ underline ] digit }

===== Comments =====
  * For //integer_literals// the exponent must not be negative.
  * High-order zeros are permitted.
  * `Space` is not permitted as `space` is a delimiter.
  * _ only serves to improve readability and does not influence the value.
  * permitted base-statements: 2,..,16

===== Examples =====
Integer-figures
<code vhdl>12     0     1E6     123_456</code>

Real-figures
<code vhdl>12.0      0.0     0.4556     3.14159_26</code>

Real-figures with an exponent
<code vhdl>1.34E-12     1.0E+6     6.023E+24</code>

Integer-figures of the value 255
<code vhdl>2#1111_1111#     16#FF#     016#0FF#</code>

Integer-figures of the value 224
<code vhdl>16#E#E1     2#1110_0000#</code>

Real-figures of the value 4095.0 (32 bit IEEE-floating point format)
<code vhdl>16#F.FF#E+2     2#1.1111_1111_111#E11</code>