Function tsvector_cmp 

pub fn tsvector_cmp(a: &[Lexeme], b: &[Lexeme]) -> i32

silly_cmp_tsvector: the size, the number of lexemes, then for each lexeme in order whether it has positions, the bytes, the number of positions, each position and each weight. A lexeme with positions, more positions, a larger position and a larger weight come first. The result is the value of tsvector_cmp.