Additional fix for :nth-child(n+B)

[super-dm3]

Pull Request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build-related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

:nth-child(n+B) selects only B-th elements

What is the new behavior?

:nth-child(n+B) selects B-th and all following elements
See: https://developer.mozilla.org/en-US/docs/Web/CSS/:nth-child#nth-childn7

Does this introduce a breaking change?

• Yes
• No

Other information

• This is an additional fix for PR #56.
  My previous PR didn't actually fix the nth-child(n+B) bug. Two duplicate functions exist for isNthChild() and parseAnB() logic. I fixed only one that passed the tests, but appearance doesn't affect the result. I didn't notice it last time.
  Ideally, there should be no duplicated logic. But it's a task for the future refactoring.
• Also, there was an invalid test:
  ...
  // BROKEN RULES -- these should always fail to match.
  // 6n + 7;
  ...
  This rule is actually valid for 20 elements. Every 6th element with an offset of 7 should match 3 elements but not 0. Rewrote this test to 6n+30 to fail

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.30%. Comparing base (5a9ddce) to head (f150006).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##               main      #60   +/-   ##
=========================================
  Coverage     89.30%   89.30%           
+ Complexity     1350     1349    -1     
=========================================
  Files            26       26           
  Lines          3131     3132    +1     
=========================================
+ Hits           2796     2797    +1     
  Misses          335      335           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.