used in the descriptions of lexical analysis and syntax.
| | | vertical bar | separates alternatives |
|---|---|---|
| * | asterisk | 0 or more repetitions of the preceding item |
| + | plus | 1 or more repetitions of the preceding item |
| [ ... ] | brackets | 0 or 1 occurrences, i.e. optional (the enclosed) |
| " ... " | quotes | enclose literal strings |
| white space | only meaningful to separate tokens | |
| ( ... ) | parentheses | group |
|
*+ |
operators | bind as tightly as possible |
|
| |
operator | least binding operator |
digit ::= "0"..."9" in lexical definitions 2 literal characters separated by three dots mean a choice of any single character in the given (inclusive) range of ASCII characters.
There is a big difference between