Conditional indications
The following rules and conditional indications are used in this document to describe the statements formats:
- Capital characters are used to indicate the reserved words; 
- Line characters are used to indicate the names, the variables, numerical or arithmetical expressions; 
- Linguistic expressions are indicated by <..> symbols; 
- Unnecessary parts of the operators are indicated by {..} symbols; 
- Alternative parts of the operators are divided by | symbol.