added documentation and tests cases for allowExpressionValues option

[V2dha]

Fixes 867

[codecov]

Codecov Report

Merging #870 (1640f04) into main (f0e04ce) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 1640f04 differs from pull request most recent head 0c19f02. Consider uploading reports for the commit 0c19f02 to get more accurate results

@@           Coverage Diff           @@
##             main     #870   +/-   ##
=======================================
  Coverage   99.25%   99.26%           
=======================================
  Files          98       98           
  Lines        1481     1488    +7     
  Branches      487      492    +5     
=======================================
+ Hits         1470     1477    +7     
  Misses         11       11           

Impacted Files	Coverage Δ
src/rules/no-noninteractive-tabindex.js	97.36% <100.00%> (+0.59%)	⬆️

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[ljharb]

Thanks, looks great!