Command of conditional generation "IF"

Syntax
<if>boolean_expression<begin>body<else>body<endif>

boolean_expression
= element<and>|<or>|<not>element ...

element
= boolean_element|simple filter

boolean_element
= p1 operation p2

p1, p2
- parameters
operation - compare operation, can be "=", "~", "<", ">" (ignore double quote)
simple_filter - can contain the next elements, always starts with "+" or "-"