-/* DIGIT = [0-9]
- DIGITS = DIGIT+
- DECIMALS = (+|-)? DIGIT* "."
- digits ::= digits DIGIT.
- decimals ::= digits DOT digits.
- decimals ::= DOT digits.
- decimals ::= digits DOT.
- number ::= digits.
- number ::= PLUS digits.
- number ::= MINUS digits.
- number ::= decimals.
- number ::= MINUS decimals.
- number ::= PLUS decimals.
-
-*/