EBNF is used to describe the formal grammar of a language. A rule has the form 'symbol ::=
expression'. If a symbol is defined by a regular expression then it has an initial capital letter, otherwise it has an initial lower case letter. Following table lists the EBNF definition.
| #xN |
N is a hexadecimal integer. a character in ISO/IEC 10646 |
| 'string' |
matches a literal string that inside |
| "string" |
the single and double quotes |
| [a-z] |
matches any character from a to z |
| [^a-z] |
matches any character outside the ranage a to z |
| [^abc] |
matches any character not among the given character |
| (expr) |
is a unit |
| A? |
is optional A; matches A or nothing |
| A* |
matches zero or more occurences of A |
| A+ |
matches one or more occurences of A |
| A B |
matches A followed by B |
| A|B |
matches A or B but not both |
| A-B |
matches A but does not match B |