Any thoughts as to why https://codepen.io/anon/pen/qVbjGa:
<form>
<input type="text" name="formField" title="Password must be at least eight characters in length, contain at least one capital letter, one number, and one special character."
pattern="\A(?=.*[a-z])(?=.*[A-Z])(?=.*[\W_])(?=.*[\d]).{8,}\z" required />
<input type="submit" value="Submit" />
</form>
wouldn't work and http://rubular.com/r/9oIgojECMf would?
You must replace the beginning of the input \A with ^ and the end of input from \z to $
<form>
<input
type="text"
name="formField"
title="Password must be at least eight characters in length, contain at least one capital letter, one number, and one special character."
pattern="(?=.*[a-z])(?=.*[A-Z])(?=.*[\W_])(?=.*[\d]).{8,}"
required />
<input type="submit" value="Submit" />
</form>
^ and $ - remove them and pattern="(?=.*[a-z])(?=.*[A-Z])(?=.*[\W_])(?=.*\d).{8,}" will work the same.^ and $ in the HTML5 pattern attribute regex, remove the anchors since they are added automatically by the engine.
[W_] and [d] @Drew?