Crate nth_check 

nth-check — parse and test the CSS An+B microsyntax

Parse the An+B microsyntax used by CSS selectors like :nth-child(2n+1), :nth-of-type(odd), and :nth-last-child(-n+3), then test whether a 1-based position matches. The Rust counterpart of the nth-check npm package. Zero dependencies and #![no_std] (no alloc either).

Parsing follows the CSS Syntax grammar strictly — the offset must carry an explicit sign (2n+7, never 2n7), as browsers require. This is slightly stricter than node-nth-check’s lenient regex; for every input both accept, the coefficients and position matching are identical.

use nth_check::parse;

let odd = parse("2n+1").unwrap();        // or parse("odd")
assert!(odd.matches(1) && odd.matches(3));
assert!(!odd.matches(2));

let first_three = parse("-n+3").unwrap();
assert!(first_three.matches(1) && first_three.matches(3));
assert!(!first_three.matches(4));

Positions are 1-based, matching the CSS :nth-child convention (the first element is position 1).

Structs

Nth

A parsed An+B expression: the coefficients of a·n + b.

ParseError

The error returned when a string is not a valid An+B expression.

Functions

parse

Parse an An+B expression such as "2n+1", "odd", "even", "-n+3", or "5".